Development Grants are just too strong and too random to exist in this game. Ofc you can ban them in co-op, but they break AI games as well by boosting you so much that you basically win as soon as you pop them. For me it not only makes the game too easy when I get them, but also ruins the immersion completely - how on turn 13 can you pay 15 damned POTATOES to a MINOR civ that should be much weaker than you and get 150 SCIENCE and 80 DUST??? I can live with that dust but that enormous science bonus just breaks the game, it allows you to do a tech per turn - RIDICULOUS. Grants are  incomparable to other special actions like migrations so that makes them total RNG as well. How can this stay untouched in the game for so long? They seriously need a nerf and NOW.

Upd: Found only 1 similar article by guys from 4x Alchemist who surely know what they are talking about. Will post the link here

Casual 81 dust and 155 science for 15 potatoes.

1 tech per 1 turn, classic turn 13.

8 times my own dust production.

Percentages have the downside that they make not-assimilating a minor faction attractive in the late game for a percentage bonus (which are very valuable!), as well as making grants more valuable to higher research factions (which is unintended).

Reducing the flat number of sensible values for the early game seems the least likely to break anything.