You can easily compare them.
Action and tab target based systems do exist and they can be implemented in different ways.
The aforementioned action based systems lend themselves to being more engaging.
However, there also exist tab targeting MMO's with more interesting combat. B&S, CoH/V, Astellia and GW2 have tab targetting systems that are more interesting than FFXIV's.
WoW manages to escape this list because even though it uses a more engaging "Priority based system" as opposed to a "Set in stone rotation" it has the ability for classes (Sans Feral Druid which is complex to maximize DPS due to buff and DoT timers) to macro a single button with all their skills in priority order and then mash that ad infinitum...
Weapon swapping isn't the biggest deal in those games, especially depending on how you have spec'd (Moreso for Tanks in ESO where you're basically stuck with SnB forever because of how much stronger its block skill is and the fact that you either need SnB or that single other skill set for access to Taunt which you need to use every 15 seconds due to how aggro works in that game)In GW2 and ESO you also need to weapon swap to play optimally to make up for the ability shortage. Personally greatly dislike the idea of weapon-swapping in combat.
Though, it's not entirely about the number of skills. But how you USE those skills.There are few (polished) MMO's I think that use as many slots as FFXIV, even most WoW specs use way less.
In FFXIV, a lot of skills are fluff ones. Like, your filler rotation of 123 for melee characters is no different to other games (Or other jobs) filler rotation of 111. Only you need extra keybinds for no reason. Heck, this is made more apparent when PvP and the RP fights will condense this 123 rotation down to a single button...
In a game like Astellia, my Assassin has a core DPS skill set of about 6 buttons. But the way those buttons are used are really interesting, making use of DoT uptime, combo point generation and usage, positioning and even mana management. With those 6 buttons, I actually have so much going on, I don't even use my filler skill.
Throw in the added complexity in that game of managing your Astels (Both their skills as well as your resources for summoning and maintaining them) as well as CC skills which are actually useful to set up for situational damage skills and you get a lot of interesting combat, without having a ton of fluff skills that are often excessive (I.e. Healers with too many heals and not enough places to actually use them. Tanks with a billion CD's but only infrequent TB's to use them on. Extra filler skills to seemingly just add more buttons for the sake of having more buttons etc)