I think solution 1 will just change the meta, not diversify it. Forcing players down any given path unnecessarily removes strategic depth from the game. Personally I'd prefer if all call-in units were inferior to their tech counterparts. I'd simply swap out shocks with penals, 85s with 76s, etc etc. I'm pretty doubtful that's ever going to happen though.
Elite Armor is a good example of this. Those panzer 4s are terrible compared to non doctrinal options. If all call-ins were on the same level, you'd see them to fill holes in armies but not completely compose them.
I do like this idea, the armored US commander is quite a good example for how this could work. Also this method means that you can instantly call on less powerful units to replace losses not vastly superior ones.
Only place this falls down is with the super heavies. You cant give all ost commanders the ability to build tigers or ele's nor the SU ISU/IS-2. For me the best thing would be to keep those doctrinal but allow them to be built from the HQ once CP's have been acquired. One the things i hate about call ins the most is how you can instantly replace super units.