Sorry to quote myself, but I think this highlights one of the issues that keeps coming back up.
If legacy paths are weak then people will ignore them, at most getting a reward for doing what they were going to do anyway, and say that it was a failed game element. If they're strong and distinct from "normal" civ-style gameplay, then people will complain that they're being forced to play a certain way. Indeed, the more specific the goals of a legacy are, the more diverse gameplay will become (because going for one legacy rather than another drastically changes your overall strategy), but the more forced it will feel. That's the dilemma. There is no difference between the game encouraging diversity by recognising and explicitly rewarding divergent styles of play, and the game "forcing" those styles of play. People claim to like the former and dislike the latter, but they're the same thing! That's why the phrase "forced narrative" is so annoying, it's a broad brush use to paint something as bad without seeing what it does. Most of the time people aren't annoyed at the forced narrative per se, just that it's not forcing the narrative they (subconsciously or not) want to tell.
I guess that one way around this impasse would be to have custom legacy path goals for every civilization. That seems implausible, and too much to ask for; making multiple parallel games is a very inefficient way of adding diversity to a single game. It's also a ton of railroading, with the devs hardwiring a particular "narrative" for each civ. The alternative is to have common goals, but multiple ways of achieving these goals. This is probably the right option to aim for, but unless balance is absolutely perfect, there will be one strategy that will almost always be optimal for each goal. But that's always what happens with strategy games.
If you really want diversity in any game, you have to ignore all explicit in-game reward mechanisms, and play according to your own internal goals. So if you want to play exploration age Inca without so much as a sideways glance at the new world, well, no one will stop you. But asking for an explicit reward for each type of role-playing inspired grand strategy would create *more* forced narratives, not fewer (as well as insurmountable balance problems).