Can you think of any episode of TOS where you could not have removed Sulu or Chekov or Uhura and substituted a nameless ensign?
Yes, there were select episodes where secondary characters took center stage, but they were few and far between. Even characters that were written out of the show and are now considered on the very periphery of Trek once featured prominently (like Yeoman Rand). Different writers had different takes on the material. It went off in different directions and at times it did feel more ensemble than others.
As far as fan sentiment goes, I would consider Trek III and Trek IV to be very much ensemble writing for the crew, and how most people would prefer Star Trek to be written. Subsequent Trek shows tried to be more ensemble (which was hard, TNGs cast was too big). And it's in the mid 80s that the anti-Shatner stuff started to hit fever pitch. So it made sense to me.