I would agree on Heavensward Monk. It was mechanically excellent. The combos were fluid and Touch of Death/Fracture gave you a degree of control to your combo progression and allowed you to delay things to save ticks on Demolish. Stormblood Monk has removed the control and depth that came from being able to manipulate your combos with those skills while many of the additions in Stormblood have a number of issues with them.
1. Brotherhood/Riddle of Fire. The unpopularity of Riddle of Fire is well known and it should have been completely expected by the devs, they took the class where the most requested feature was a fourth stack of a haste buff and they made it slow down instead. At first glance they obviously wanted to pair the slow from RoF with Brotherhood so we wouldn't actually feel the slow because of how much oGCD weaving we'd be doing. The problem is even with optimal compositions you only really average 2 Forbidden Chakras from Brotherhood and Monk doesn't have the massive suite of oGCDs needed to fill the time created by the slow so you just dump everything and feel really sluggish. It's a bad feeling and absolutely not what I wanted from playing Monk. Brotherhood has a separate issue where it's hyper reliant on party composition to provide a mediocre number of Forbidden Chakras, so it basically is guaranteed to whiff in any 4-mans where the absolute best case scenario is having half as many physical DPS as you actually need. I would love it if this skill just removed the requirement to spend Chakras on Forbidden Chakra for its duration so Monk actually felt decent to play in dungeons, but I doubt they'll make such a change.
2. Monk's tools for maintaining Greased Lightning are incredibly situational, usually on long cooldowns, and outright worse than the tools other jobs have for maintaining similar Buffs. Examples: Enochian. It's as essential to BLM as GL3 is to MNK, it has a Relatively long duration, and through the preexisting Transpose and the Enochian oGCD, they can maintain the buff throughout the entire fight indefinitely without losing their Umbral Heart stacks. If they do lose it they can regain it instantly every 30 seconds because Enochian's cooldown is short. Ninja, similarly has an incredibly long duration on Huton and refreshing it is fast with Armor Crush. Dragoon has a long duration on Blood of the Dragon and that can instantly be extended by hitting a button they already had and if its lost the button to regain it is still on a short cooldown. They lose Dragon Eyes but with the recent rework the loss of the Life of the Dragon Phase is Mitigated.
Monk, comparatively, has the shortest buff in the game, and rather than having the tools we already have improved to maintain it we received a new action; Riddle of Earth, which already puts us behind BLM and DRG. Unlike the tools that BLM, DRG and Ninja which work entirely on the Players ability, Riddle of Earth's refresh only procs off enemy damage which when coupled with Greased Lightning's incredibly short duration can make your stacks fall off before you actually receive damage depending on where you are in the combo (Final Boss of Ala Mhigo, Final Boss of Shisui of the Violet Tides, Shinryu's charges in Normal and Extreme). It also can require Monk to eat AOEs it normally shouldn't, many of which grant vulnerability stacks (Shinryu Charges, Several Rabanastre Bosses). Worse, this ability is on a 60 second cooldown and there are several fights where you will need to refresh your stacks because of an invulnerability phase where you can't because the ability is still on cooldown (3rd Boss of Rabanastre comes to mind). This ability should not exist at all. If Monk had received equivalent care during the action rework, it would have received a change like Form Shift Automatically refreshing Greased Lightning if you went from Coeurl Form to Opo Opo form to make GL3 Management as Easy for Monk as Enochian or Blood of the Dragon Management is for Dragoon. Instead we got a hyper situational ability that sometimes can't even be relied upon because of its cooldown. Compounding this is Perfect Balance. While Enochian and Blood of the Dragon are on 30 second cooldowns. Ninjutsu is on a 20 second cooldown. Perfect Balance's cooldown is nowhere close to that, it's 3 minutes long. 6 times as long as the next equivalent buff.
All this together just screws Monk in content where other Jobs have less issues comparatively.
3. Monk has an enormous number of highly circumstantial actions that see so little use that they may as well be useless or actions that are actually useless. On the topic of this thread are the Fist Stances. Fists of Wind and Earth currently serve no purpose ever. It is actively more detrimental to use them than it is to remain in fire eternally. Tackle Mastery by extension is a useless trait. One Ilm Punch's form requirement prevents it from ever being used to stun anything, as does Arm of the Destroyer's requirement make it difficult to stun anything. Tornado Kick's cost is so massive that it is rarely justified to ever use it outside of the boss being at <.5% health, and because we need to at least try and save our stacks it's often better to just ignore it or use Riddle of Earth. Our TP sustain is infinite now, even without Riddle of Fire's slow, so there's no need for Purification in single Target and Monk's AOE sustain is so strong it often isn't needed in AOE situations especially if your co-DPS is actually AOEing or brings Goad/Tactitian. Arm of the Destroyer's AOE damage is massively weak for how much TP it costs, it takes Five Targets to barely beat Bootshine in potency for almost three times the TP cost. Outside of super massive pulls that rarely occur in dungeons, Arm of the Destroyer sees no use.
4. Monk lacks a lot of basic quality of life things other Jobs have. It doesn't get a ranged GCD at low levels for single mob pulls. Monk's mobility is terrible, we only have one mobility cooldown and we have to use it on cooldown to deal our maximum damage. Ninja and Samurai never have to use their gap closers to achieve Max Damage. Dragoon, while it does need to use its jumps to achieve Max Damage and build eyes for Life of the Dragon, also has Elusive Jump which allows a great amount of Free Movement at no cost. We don't have an AOE chakra dump, so we have to dump Forbidden Chakras on single targets in AOE situations. The previously mentioned comparative difficulties in maintaining Greased Lightning through both its skills and the long cooldown on Perfect Balance compared to similar skills would also fit under this. Our Aggro generation is insane and while Diversion is useful in limiting it, it's cooldown is too long to be effective, we could very much use an aggro 1/2 Skill. Overall there's a lot of changes that Monk has been waiting on for a long time that it should have gotten in Stormblood that it just didn't get.
This list of complaints also isn't all inclusive but they were the ones I could think of at the time of writing. I have certainly made other points in other posts I have made on the subject of Stormblood Monk that I failed to mention here.
Even if Monk had a solid design in ARR, there's been nothing done to expand upon it which is what many people have been annoyed about. The finest meal in the world will really quickly lose its appeal if its all you've eaten for a long stretch of time and Monk is the same way. It's been identical for far too long, and to a certain extent there's a degree of jealousy towards other Jobs as well. While we're doing the same things we've always done, Dragoons now have Nastrond and Life of the Dragon, Ninja's have a Frog/Ninki Nuke, Machinists are Flipping around like they're in a John Wu movie, Bards have the gate of Babylon, Black Mages have Foul, and Summoners can literally summon Bahamut. I want to do new things, I want some new way to punch enemies, or launch Ki-blasts.
The most recent action we got that we can actually be really enthusiastic about was gained at level 54 with Elixir Field and it doesn't truly change how Monk functions, it just kinda slides between what was already there. There's a desire for something new with Monk and a large number of long standing complaints that we were hyped up to believe would be addressed with the action rework that just didn't get addressed at all. It feels like they've gotten to the point where them being completely unwilling to touch the core of the class is a problem, not an asset. In Heavensward even if most of what Monk got was Quality of Life, it was good Quality of Life and we also got Elixir Field to sweeten the deal. Form Shift? Awesome for maintaining stacks in short downtime phases. Meditation and Tornado Kick? Great for mitigating damage loss when you lose your stacks. Purification was the only skill that was kind of lack luster. In Stormblood we didn't get anything new or even anything all that exciting. We got more Quality of Life but it was decidedly worse than what other Jobs got and it took an extra skill slot to do it(Riddle of Earth), promises of fixes to many longstanding complaints that didn't get addressed (the action rework that was the main selling point of the expansion), a trait that doubles down on a long standing design issue with Monk (Tackle Mastery), a skill that literally replaced a skill we used to have in Cross Classes with an effect that's damn near universally reviled (Riddle of Fire), and a raid buff with a personal DPS interaction that while a good idea in concept really doesn't feel that great in practice (Brotheerhood and Deep Meditation to an extent).