Do not force level caps on content - You segregate the player base

[Jocko]

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You can't have your cake and eat it too. You can't please everyone, and you can't design a game around working with every possible preference. You have to pick a direction and fully devote yourself to making those design decisions as fulfilling as possible

Go on, try seeking a party for baby Ifrit and requesting only members of the appropriate level. Actually, I'll save you the time and tell you what'll happen: You're not going to get a party. Why is this? One, due to the pace of leveling, players at that level range are a vast minority, and two, there's no incentive to play a level appropriate class when you have maxed classes. It simply won't happen.

Now, if there were caps with rewards for completing the quest multiple times, the content is properly balanced and people make constant progress, whether they're completing the quest, or getting seals/money/whatever for helping another. Throwing that all away because some people 'like cheesing content' is foolish.