The penetration changes for the Churchill and Cromwell aren't necessary. Reducing their penetration (to T34/76 levels) by 15-25 reduces their scaling significantly. It's especially egregious on the Churchill as the Cromwell can, at least, flank. Against the Panzer IV, this becomes a 8.33-13.89% decrease in their ability to penetrate its frontal armour (which was already a 75% chance in the best possible conditions). In addition, the USF Sherman has exactly the same penetration and costs the same amount as the Cromwell.
The fix to Tommy vet 3 is simply uninteresting. I'd prefer another solution.
The weapon rack change doesn't address the big picture. Tommies already receive worse veterancy and a worse LMG. They need both Brens to have the same percentage scaling as an LMG42 Grenadier squad, especially with veterancy.
1)churchill with 105-135 penetration, 1280 hp and 320 armor will reliably beat a panther one on one. However, if the penetration was lowered to 80-120 then the panther will win. Durability and HP are more important for the churchill so I nerf the pen instead. The new churchill will still reliably beat the panzer4.
similar case with the cromwell. I prefer the cromwell to keep its small size in exchange for lower penetration. As you said the cromwell can flank to get around a lower penetration, and the small size help it survive against the axis late game. the 23 size cromwell and sherman are just too easy to kill. I doubt a size 20 cromwell will fare much better.
2) the scoped lee enfield is nice to look at, I don't think it's worth the problem of keeping the look.
Your solution would need to make "exception" for every pick up weapon in the entire game. It's not enough to just account for the british pick up weapon. There's also an additional fact that every tommies except for the gunner will be using a scoped lee enfield at vet3. That's just gawky.
3)the tommy doesn't need the same percentage increase in dps as the grenadier. The tommies are probably the most durable squad once they've gotten their fifth man. The grenadier are well known to be fragile. The tommies are the stonewall to the grenadier's glass cannon.