I would like to see veterancy bonus removed from basically everything. The only reason to keep it for ACUs is because it would be hard to balance the game where people expect ACUs to get those bonuses.
There is no reason why robot armies would "get smarter" from veterancy, or why individual units would benefit. If the AI actually is learning from experience, the entire army should get stronger. It isn't consistent with the Supreme Commander "backstory."
The game designers originally had veterancy different, it was based on the number of kills rather than the amount of mass killed. They said the reason they did this was to punish players who spammed too much t1. They wanted to create a mechanic to punish t1 spamming in order to encourage a different style of play. It was a bad reason to add a game mechanic and the mechanic itself was done badly. Doing it based on the amount of mass killed is better, but it still just doesn't belong in the game at all.
If we get rid of bonuses, the only reason to keep track of "veterancy" is sentimental, so you can look at a unit and say "wow, three stars, this little striker did a lot, what a hero"
We should not be afraid to lose this particular game mechanic. FAF already has a lot of mechanics, probably too many. Sometimes, cutting something is better than adding more stuff. The veterancy bonus mechanic just isn't needed.