You're equating frontline usefulness with being a mandatory tech progression(since vanila factions can't tech without them) and that is not very valid comparison.
Sturms carry early game well and are REALLY good at repairing, you don't need to have more then 1 for unit to be useful and you feel how useful and important the unit is when you lose it.
I do agree REs do not have as much importance, but they still make an excellent bazooka platform and that Pershing obviously isn't going to repair itself, mine sweeping is invaluable regardless of game mode.
1. My other post is where I make my main point but I'll try to explain it again.
2. I'm not making a balance argument. I'm not saying that they are good or bad. Sturms are the most essential unit in the game pretty much. But you should rarely have more than 1. So the point is that Sturms and REs don't play any role in build orders because there's no reason to have less or more than 1 which reduces macromanagement complexity. They are pretty much never a build option unless you lose them in which case you HAVE to rebuild them (which isn't great either).
3. What Hannibal is saying is wrong. It's a very significant decision whether to reatreat your pio early or wait for it to retreat "naturally". If you rush a 222 a lot of the time you will have to retreat your full health pio after about 4 mins. If the Soviet wants to rush a T70 he will have to sacrifice either sweeping capability (which is significant considering T70 could run into tellers) or a big part of his combat strength (flamer) for a while. THOSE are interesting trade offs. They are just examples of the general principle I'd like to see applied in CoH3.
4. You could follow that principle for every faction in CoH3 but it's not necessarily unbalanced if you don't. It's not inherently problematic if one faction has a certain mechanic that is (dis-)advantageous. The whole "unfair" argument only applies to the accecss to basic tools like anti building/indirect fire etc.
Edit: I think you should reread Hannibals quote. You agreed with him but he seemed to be saying somethign entirely different from you. His point was that it's not really a meaningful decision anyway when to reatreat your pio for building base.