Again, it really depends on the player.

If you're doing a brand new fight, you have no idea what to expect. When a new tier releases and players go to unlock Savage, they make guesses based off what they see in normal. Part of the guesswork involves trying to adjust your comp in anticipation for what you think you'll see. Guess incorrectly, and you might be at a disadvantage until the next lockout.

The role action system, as it was released at the start of Stormblood, addressed some elements of that. It doesn't really matter if you didn't happen bring a PLD and BRD to silence a particular mechanic. You can talk to your teammates and get someone who is comfortable with the mechanic to swap in the action. You might say "Why don't you just give everyone a silence, then?" But figuring out the correct loadout is part of the puzzle. It's only trivial if you read the answer after someone else has solved it for you.

But I think we can add a bit more depth to this. Interrupts are pass-fail mechanics. There are other decisions that are a bit more grey.

Consider the present system of physical and magical tankbusters. Many fights will have a mix of both. But instead of having this be a job level decision (i.e. do I bring DRK for Dark Mind), what if it was an issue of "Do I bring a physical mitigation cooldown or a magical one from the role actions list?" Now you have to look at the fight, which tankbusters are physical and magical, and see what choice best augments your rotation. You can still work around a bad choice, but a good choice will make your life easier.

If you're the sort of person who is looking up a guide to figure out what's optimal, then it's naturally going to be a chore. But not every player fits this category. Some people read guides, others write them.

One thing that hasn't really been explored is the idea of trait customisation. I'm thinking of something akin to Warcraft's Major and Minor glyph system, which allowed you to tweak your class in small ways. Do you want a slightly shorter recast on your gap closer or a proc that resets it? Not every customisation option needs to impact gameplay either. Some things could be cosmetic (perhaps reskin Rampart as Shadowskin, as an example).