I am not 100% sure without the context of this discussion but I guess it is just as you think. Some traits are very strong on the first piece but suffer bad diminishing returns when you have them on more than one piece.
Fury of Xuen or Glory of the Dawn for WW monks are examples for that. DKs are mostly fine though (except for the weird case of Icy Citadel where the third stack far outshines the gain of the first two).
Generally Bloodmallet is a good resource to check which traits to go for in any situation:
https://bloodmallet.com/index.html