From my point of view, altering TCs so that having 1 or 2 in a base doesn’t completely invalidate real-world combat experience is both good game design and more realistic.
In ‘real life’, no military organisation on the planet recruits a soldier into their equivalent of the SAS until he has proven his worth through high-level experience in battle - because until he has done that, he hasn’t gained the instincts needed to survive in a split-second life-or-death environment.
So Training Centres should enable you to train up new recruits to a level where they are likely to survive if you send them on a mission (say: Lvl 5), but no further. In addition, they should be balanced so that if you have only 1 TC in a Base, it levels up more slowly than if you are prepared to risk your troops in combat. It doesn’t NOT level them up - it simply does it at a slower pace than the current system.
To those who say: ‘if you think TCs are overpowered, don’t use them,’ I turn that statement around. If you really want to buff your new recruits without risking them in battle, you should be prepared to put in a higher investment up-front for what you see as the long-term benefit of getting top-level soldiers essentially free of any risk.
If TCs gave half the points they do now, you would still have the option of building 5 or 6 of them in a single dedicated Training Base, which would give you exactly what you’re asking for - but it would be a choice to do that, rather than a no-brainer, which it is now.
I would also add, that under A different way to do difficulty modes which I am proposing on the Feedback site, both sides could get what they want: if you want OP TCs, choose CHARACTER or SUPER-SOLDIER MODE, if you don’t, choose TACTICAL. Everyone’s happy.