Q: "So, can anyone explain why the "OP" companions were a bad thing for everyone? "
A: if you played since 2003-2005 continuously MMOs you would notice that most of them are of so called "theme park" kind - where developers work hard to provide some "content" for players. In return players pay something,somehow to developers. And all of them suffer tremendously from one common problem - developers can't generate content as fast as players can "eat it", hence developers attempt to slow down as much as possible game pace and increase the playable time for players. The same award program that kept people to not drop their subscription before 4.0 was implemented in every other MMO. especially WOW - Blizzard went as far to gift D3 to people subing for whole year (!)
You could search for another post in this forum, if not deleted already for another player who transposed his observations from other MMOs over SWTOR - drawn some conclusions and BioWare marked him as data miner (Big time ).
As British gov says - Keep Calm And Continue The Grind Of Affection.
edit: so it is bad because Devs can't keep up with customer demands and produce garbage, and players experience huge gaps between content patches.