Right direction and good changes, but it needs some more. My suggestions:
All of these nerfs are going to once again make the UKF unable to compete lol
1. The AEC isn't really a support vehicle, it's more of a proto panther, otherwise it wouldn't perform so poorly against infantry. The reduction in range and damage is to much of a nerf. It takes 3 AT shots to destroy an AEC, and it takes the AEC 2-3 shots to destroy a scout car. I think that's pretty fair since the whole point of the AEC is to hard counter light vehicles, which the sight range is going to already make it less punishing. The AEC is also easily hard countered by double shrek PanzerGrens with their heat seeking missiles that can shut down a 60 fuel costing AEC rather fast. (And ignoring it's still inferior against a Puma) With the exception of the Churchill, the UKF is already lackluster with vehicles. At this point, there's less justification to get an AEC that will delay a Cromwell. Also i'm sure most players arent going to use the AEC late game, so it's not like returning it's damage output at vet 3 is going to be a huge service. The AEC should keep it's current damage output, or at the very least have any nerf replaced with a good compensation in something else.
2. The mortar pitt is indeed expensive. Especially in the early game. It's plastered into the ground and unable to avoid barrages or advancing tanks. They're easily countered by indirect fire or arty. For this I can't agree with the stated nerf suggestions. It's already a little bit of a high risk unit when it can be easily destroyed by a panther charge of stuka, or some OP off map call in.
3. The UC is still fragile, I don't see how it can be comparable to a tank. It's life expectancy is depleted the moment Pgrens or a 222 roles in the field anyway. Heck, I've seen it's health wither fast when Assgrens managed to charge it. It's the UKF's only starting option to counter MG spam. the whole point of it's original armor increase was so it wouldn't die when trying to burn our garrisoned MGs. If nerfed, Brits won't have an effective counter to MG spam. If such a nerf were to happen, it should have an ammo costing option to have it's full armor returned like with the USF's utility car's armored skits.
4. This is actually something I can agree with. Tommy blobbing is just as cancerous as MG spamming, and a starting engineer team does change the dynamic a bit