Edit: I digged out the patch notes:
“Any secondary stat that the target piece already has, which is lower than the corresponding stat on the source piece, will be upgraded.”
Later in the thread Riley stated:
“The only thing that has to match for the Infusion is the gear has to be for the same class and same slot. Other than that the rarity can be mistmatched.”
So yea, there must’ve been a change, and likely a recent one since we just had an evening to help a tank up his vitality and practice, using the queue, before goin into harder/shard stuff.