UKF and also USF side techs (even USF ambulance) are a mechanisms to move costs from the main tech branch. Especially the pure UKF main tech path would be stupidly cheap otherwise. Axis also unlock upgrades during their main tech, meaning parts of their main tech cost can be attributed to unlocking the upgrade. Long story short: Counting Allied side techs towards the squad cost does not make much sense.
I don't know where you took this idea from. USF was meant to be versatile with superior infantry you could decide to upgrade at side cost to be more powerful or keeping them being over time on par with cheaper/upgraded Axis infantry and relying on LVs or fast medium tanks.
When people complains about how boring 3xRM is every game, that's because the decision making part of USF BO was never meant to be on the units you build but side techs used you unlock.
What went wrong with this design is that upgrading RM which were already superior lead to inevitable snowball effect every game.
Today we're far from here, we're at a point where RM aren't naturally superior anymore to any other infantry and their side tech are mandatory for them to compete because of the many balance decisions taken over time with little reflexion on the impact with USF faction.
Today more than ever, side tech must be taken in account in RM's cost. One of the reason Airborn is popular isn't only because Path but also Para which don't need any side cost to be equiped with LMG and grenades.
Side tech aren't gate, they were optional at the beginning and now mandatory. And this is because they are mandatory that the USF design as a whole is broken today.