Re: The gap between Zeo and TAPRM - your headcanon?
 

I don't think the powers grew too strong for them to use. While the Zeo Crystal grows more powerful over time, it's probably only charges when it's whole. Not to mention that Zordon meant centuries and millennia, not a year or even a few years.

In essence, the Zeo Rangers were taking power away from the crystal faster than it could charge.