The Who and Led Zeppelin were not power trios because they had four members. By definition, a trio has three.
Wikipedia says a power trio is "
a rock and roll band format having a lineup of electric guitar, bass guitar and drum kit... leaving out the second rhythm guitar or keyboard instrument... that are used in other rock music bands that are quartets and quintets".
I'd add another caveat in that usually in a power trio, all three musicians are virtuosos. There are no passengers in a power trio. For example, even though The Police was pretty much all about Sting, Andy Summers and Stewart Copeland were very good at what they do and were a vital part of the band's sound. Cream, possibly the epitome of power trios, was the sum of three amazingly talented parts.
Being a busy bass player can work in a trio, as it can fill in the spaces left by the "missing" instruments, and you can make it part of your sound. But making the band all about you, making all the decisions, wanting to get your way, having all your non-negotiable terms and conditions... that's a great way to break up a band, and more likely your friendships too. I'm glad I'm not in a band with you.