I think Grenadiers are fine.
The issue is mainly the Brits. The "Bolster Squad Package" which is like a weapon upgrade for everyone, is cost effective, comes early. Maybe they should halt it for more later. Change something because Brits usually do have the upper hand.
OR
Give indivdual upgrades for a to Bolster Squad similarly to the Wehrmacht "German Infantry Doctrine". This will fix issues especially what OKW suffers from since they get easily outmatched in the beginning.
(Depends heavily on map also, if it is urban, lots of buildings, Brits dominate).
...
Here is how I also see it
Bolster Squad costs ammo (60 ammo or less), limited to 1 Bren (45 ammo) only
Without Bolster upgrade, can get 2 Brens.
It will increase diversity, either going for more durability or more firepower. Diversity is important. I think this is what needs changing. No buffs required personally for Grens, just nerf the UKF Tommies specifically. Something needs amends
Be interesting to see what blister tied behind anvil (any maybe a 3rd weapon slot in hammer? Idk)