I think "illusion of choice" gets incorrectly applied to a lot of situations where there actually is a legitimate choice. It comes to down to whether the choice is being made on objective or subjective grounds.
It's valid for something like simple gear choices and simple stats. If I'm a DPS evaluating two pieces of gear for a slot, neither one of them changes how I play the class (this part is important and I'll come back to it in a bit), and one of them will make me do more damage than the other, the choice here is clearly an illusion. I have the option to "choose" to use the piece of gear that will make me do less damage, but since my goal as a DPS is to do more damage, there's no reason to do so.
Choosing between two different classes to play, however, is not something that can be simplified to a correct or incorrect decision. FFLogs shows monk having generally higher DPS than dragoon, but if someone is personally better with dragoon's rotation or enjoys playing dragoon more or is in a group where someone else is already playing monk then the correct decision may be to play dragoon even though monk has the higher DPS potential. There's no illusion to the choice here; both options have pros and cons.
I mentioned above that it's important that a piece of gear needs to not change the way you play a class in order for the choice to be an illusion. I say that because it's perfectly possible to have gear that presents genuine choices, but it usually requires more creativity. Take bard, for example. A piece of gear with an effect like "Raging Strikes Effect +5%" is probably going to end up being either superior or inferior to the alternatives. If it's superior, you'll use it, if it's inferior, you won't. It's a more interesting stat than Determination or Skill Speed, but it's still probably an illusion.
But what if you had a piece of gear that changed how Wanderer's Paeon worked. Instead of +30% damage and moving interrupting your casts, what if it now gave +20% damage, allowed you to cast while moving, but added a 50% heavy effect? Or if you had a piece of gear with noticeably less DEX than similar gear in the tier, but it slowly accumulated up to three charges and each charge let you move without interrupting a cast once?
Now you're making a choice between higher damage and increased flexibility. If you're skill and comfort levels are high enough that you can manage your rotation perfectly in spite of the mechanics of a given fight, you're likely looking at the first option. But if you're new to a fight or there's a mechanic you have trouble with, maybe the other options would let you personally do more DPS by reducing the penalty of movement.
Yes, but I'm not sure that changes anything about what I said.
Unless no alternative route to completion exists, the best way is not the only way.