Very good changes.
My critiques:
1. USF desparately needs a sniper counter. Possibly an upgradable snipeshot ability for either the captain or the RE?
Maybe a doctrinal option like redesigning pathfinder as support unit at 240 manpower cost and making critical kills a timed ability with 40-45 range?
2. Without having tested it (there's a lack of players willing to test the mod unfortunately so I personally have only tested soviets and wehr) the Scott change seems like an overnerf. The scott can be problematic but its strength strongly depends on the map and the army compositions. I see the problem that it can be nearly uncounterable (similar to the sniper) in certain stalemate situations that tend to occur on maps like langres and crossroads or on crossing in the woods in 2v2. But fact is that this unit is fairly rarely seen in 1v1 games simply due to the fact that it brings you one medium tank/td down in an even game. I feel like with this change it would basically go extinct in 1v1. I also don't understand why the vet 1 smoke isn't removed as a first step towards decreased survivability.
Agree
3. WC51 nerf might not be enough. The low cost of the WC51 and the super strong doctrinal context would probably still make it the go to option for USF. It will still fight infantry super cost efficiently early on. The exposure to small arms fire won't make that big of a difference because it can self repair without any costs. Unlike with the Bren Carrier you don't give up any capping power using it. And it still has the mid game utility of functioning as a bazooka/satchel carrier or mark target deliverer.
WC51 should lose the crew that cost more than half the price of the unit.