To be honest, these points here are a lot of what's wrong with this thread. In order-
The immediate reaction to SAM numbers being so high, is that either they're too strong, or it's too easy. It's an assumption, and hardly a fair one. By that logic, I guess SMN and MCH were either too powerful, or too easy in Creator Savage's patch, since they topped most of the charts, right? It's about as baseless as can be.
Yes, decision making and on-the-fly math/judgment calls make SAM difficult. No, it's not meaningless conjecture, or dummy situations. For one, I can't use Third-Eye>Seigan on a dummy. It entirely depends on my knowledge of a fight, if I get chosen for a mechanic, or if I'm predicting a mishandled mechanic (Seigan is unlocked as a proc after being hit with Third-Eye active). Anyone arguing that SAM is easy never mentions maintaining maximum uptime of this 15 second cooldown ability, and how efficient it is, potency wise, per resource spent. Something that sometimes won't matter if you don't get chosen for a mechanic, but will if you do. Using this ability leads to overall higher DPS because it allows for more resource to be used over the course of the fight.
In Susano, getting chosen for the rock, or rooted as a lightning changes things drastically as well. As given with the previous example, if chosen for one of those mechanics, how will you deal with not wasting a resource you've gained? Similar in concept to using a weaponskill on WAR in 2.x/3.x with maxed Wrath/Abandon, Sen should not be stacked. What do you do, then, if you are chosen for one of those mechanics, and you DO already have a Sen active, but need your buffs from the corresponding Sen combos? Since your buffs are tied to Sen, you either waste that resource, or find a solution for not wasting them. And all of this is going on while you're doing mechanics, watching your Kenki to make sure it doesn't hit too much of a surplus, while watching Hagakure in relation to your current Kenki to make sure you don't go over 100 Kenki when you use it, while watching how many Sen you have, just in case you need to reapply your DoT before consuming Sen with Hagakure, while watching Guren's cooldown which costs half of your gauge, while making sure you only use Guren at 70 Kenki if you're coming up on a Midare so you can have 20 left over for another ability, while making sure you get max uptime on Third-Eye>Seigan. Oh, hitting positionals too. Oh, and cast times on Sen abilities, while trying to dodge AoE's, or place yourself for mechanics, or place yourself for positionals before the cast.
We can't talk objectively, so I can only give opinions on why MNK ends up easier. I'll decide against that though, because ultimately, I don't want to get into min/max type of conversations about MNK. The better conversation, is that with min/max talk, ANY Job can be seen as having complexity. I've raided as NIN, MNK, and DRG before SAM. I've looked at the guides and documents for BLM. I've dug through SMN documents with pages upon pages of math and details of the best rotations for different situations. Every Job in this game operates on that same idea. There is skill in bringing out the maximum DPS of any Job in this game. The varying degrees depend on how much you personally care about jumping down the rabbit hole, and how difficult the Job feels for you. If we're gonna start nerfing/buffing Jobs based on feels and assumptions though...
And you should care about the identity of a Job vs. your own or others. That's the thing. As DPS, it's hard to really differentiate one from the other as far as identity goes, because the ultimate goal is to demolish everything, it's just how we go about it, right? It's easy to understand why PLD shouldn't do more than MCH. It's a tank, that's not it's goal. However, we've gotten to a point where some DPS have support (in differing ways), and others don't. That creates precedent for analyzing the identity of a Job, since that will better balance the sum of it's parts. Not to mention, sometimes the identity of the Job contributes to the ultimate balance of it. SAM, and BLM being the best examples of that (and BLM needing some love in that respect as well). If you don't care about that, then we should just play a game where no DPS Job has any identity, get rid of all support skills, and just press blank icons to see big numbers, because that's the only thing that matters on a damage dealer, apparently.