I can't really talk about how exactly the initially released faction played since I only played bot matches with friends back then and did not care about actual balance. What I can provide though is logical reasoning about the state of the last 5 years, which in overall design has not changed an awful lot anymore.
Your main point from what I get is that Rifles would not be competitive without side techs, therefore the side tech cost needs to be added to the squad cost.
I agree with the first half, not with the conclusion. I'd actually see it exactly the other way.
I'd first refer to
Gachigasm's post about overall tech cost. The main point is: UKF and USF tech cost, neglecting all other fuel expenditure, is very cheap, way cheaper than the costs of Axis. Let's assume the following:
1. Current state: Cheap main tech, side techs not optional: Medium timings are roughly the same for all factions
2. Cheap main tech, side techs optional: UKF and USF factions would gain a massive advantage by pushing out mediums as early as 11-13 minutes, depending on the faction
3. normally priced main tech, side techs optional: Not the case. In this version medium timings stay similar, Allies might gain an advantage in infantry combat.
4. normally priced main tech, side techs not optional: Allied mediums will come later than currently.
Considering all this, and disregarding if we think it is good design or not:
Allies are supposed to get their side techs, and the cost of their main tech is cheaper than Axis' to account for that. Other approaches would lead to imbalances, at least with the current performance of units.
This does not answer the question if this cost should be added to squad costs or not. In my opinion, definitely not, because:
1. Axis also pay for their unlocks, but they pay for it bundled together with their (more expensive) main tech. A certain amount of this can be attributed to being able to upgrade weapons, like Allied weapon racks. How much you'd split to that is actually fully arbitrary and does not help the discussion at all.
2. Assuming you'd add the costs of Allied side techs to infantry squads, this means that UKF/USF main tech is pretty cheap, since you already attributed the cost to the infantry.
3. How would you even attribute the costs to individual squads and what are your conclusions from that? USF racks act on all infantry squads including crews, grenades on some. Do you just divide by the number of squads? What if you lose squads and replace them? Do you account for that? Does your Riflemen squad suddenly become cheaper and they have to perform worse because the cost got split across more squads?
4. The game has no win condition by teching. This will be a bit more controversial, but: Adding side tech costs to infantry by logical extension means that you need to add "main" tech costs to vehicles. This point ties in to points 2 and 3. UKF/USF would have a very cheap first medium then.
Anyway, all these points basically argue one thing:
Adding tech costs to units and concluding any strength comparisons is nothing but arbitrary and leads to basically nothing being comparable anymore. Tech costs determine the timing of units, the unit cost the strength.