I agree on giving UKF free nades and weapon racks upgrade with platoon unlock for the cost of sacrificing one weapon slot. That would bring them closer to the versatility of axis inf.
So lets get this straight:
British Unlocks for what you describe:
Tier Upgrade which requires nobody present at base is...
30 fuel 180 manpower = Tier 1
10 fuel 100 manpower = Grenades
15 fuel 150 manpower = Guns (on any squad not just grenadiers)
35 fuel 150 manpower = 5th man on the squad
45 munitions = 1 bren ( on any squad of your choosing )
I'm going to leave the 5th man out, because that's obviously late tier and Grens don't get access to it.
Total cost is 55 fuel and 430 manpower.
Now lets look at OST:
10 fuel 80 manpower: Tier 1, you know, so you can build more than a pio or an mg
40 fuel 100 manpower: Tier 2 research
20 fuel 200 manpower: Tier 2 building, plus send that pio home to go make it
60 munitions = 1 LMG on a grenadier only
Total cost is 70 fuel and 380 manpower
Don't forget both UKF/OST infantry love fighting in long range fights in cover. But IS can build their own cover, OST needs the pio to do that for them.