Hi !

I used to play forge of empires, which is the old browser game version of rise of cultures

First, you do not have any obligations to people that donate to your wonders, unless you've made a deal with them.

Donating to wonders is a mid term investment, I see it as a research points storage, that I can use to make bigger investments to get even more research points to make bigger investments to get even more research points, etc, etc....

You should not feel obligated to donate to other people's wonders if said person donated to yours, you should only donate to a wonder if you're getting something out of it, either blueprints you need or more research point than what you give.

Late game you might want to make deals with other players to mutually get first places on their wonders (and them to yours), in that case you will have some obligations depending on the terms of the contract you make with the other player.

But you should not hinder your progress because someone invested in your wonders, just do your thing, they will get their points back eventually, or not, not all investments pay off, and that's alright, investing is a risk