No, no one HAS to apply themselves. But think about that for a moment. . .

I don't feel like making effort. . .
You don't feel like making effort. . .
Those other 2 guys in the party don't either. . .

So what then? Nothing gets done, the party disbands, someone complains "it's too hard" or "I can't clear this (because I'm not trying and no one else is either)". . . And the bar. Gets. Lower.

Welp, see you in Stormblood. I suppose the most exciting endgame experience will be Kugane hide & seek, or something.