Okay, how about this.
We keep IS performance at 4 men appropriate for their cost - as much as a rifle squad with less of the padding. Make them cost a more suitable amount to reinforce.
People who forget history are deemed to repeat it - that line couldn't be anymore true with what you're suggesting here, it means ost utter dominance through sniper attrition.
It also provides upgrade that isn't worth the cost anymore.
Bolster is then a late game upgrade which improves durability against explosive weapons and reduces reinforcement costs, akin to how the 7 man conscript upgrade functions.
Con function is a replacement for no stock weapon upgrade, but instead of all out DPS boost of a weapon upgrade it provides couple of bonuses that ensure cons can win attrition war in small arms firefights.
Bolster isn't really comparable here as its supposed to enhance survivability and performance of least numerous british infantry, so instead of getting 1-2 more squads, they can focus on existing 2-3, your suggestion completely ignores that fact.
You can rush it against snipers or delay it if you don't need it right away. It can get a cost adjustment if it needs it, or be bought a squad at a time.
It also creates convolution, requires new weapons and weapon profiles to be implemented, requires switching them, ignores how that would interact with weapon upgrades and forces rushing the upgrade against ost because it would be incerdibly stupid not to build sniper to bleed them early game while having easier time to prepare for now delayed vehicles and tech due to need to rush the upgrade.
In short, it adds a shitload of problems and fixes nothing.