Amplifier towers were considered substantially overpowered before, so they were up for a nerf or possibly simply a removal of the mechanic. The alternative we went with was to let the new "no rebuilding" rule function as that nerf; they're now a temporary boost that you get from between the time you purify them to the time that the overlord stomps them. You can't stop that destruction but you can control the timing of the purification to correspond with a time that the overlord is occupied several turns away (which is also something you can influence, though it's more of an advanced thing), giving you several turns to exploit the amp tower advantage.
They've also been indirectly buffed by the reduction in average world size.
All that said, feedback is welcome
Just explaining why we did what we did.
