The Mesoamerican civilizations, Corea, Mali, Khmer & Indonesia will vassalize all too readily.
But that is normal and I don't think should be changed. As they normally don't amount to much;
vassalization helps them survive and contribute something.
I once had a Rome game where I had Inca as a vassal; I tried actively to keep them less advanced,
but they managed to catch up to me and overtake me briefly before Future Tech, without Internet.
Big civs like China, Russia & Mongolia no longer vassalize as much or at all,
even if they're down to about one city/on the brink of collapse from being under siege and you've got Astronomy.
The rebirthed versions, while usually weak, will never vassalize to the player and usually end up vassalized to someone else like Mongols or Vikings.
Most of the European civs will fold/vassalize under normal parameters.