I'm not saying TMP is a perfect film. I agree its pacing is too slow. It needs a heck of a lot better editing than even the Director's Edition provided, for a start. But TMP was a film that at least tried
to be about "high concept" science fiction ideas. Even if it failed, or only partially succeeded, it did try. And many of the other Trek films tried, to one degree or another, even while improving the pacing and adding more action/adventure elements.
My point, though, is that a major studio wouldn't make such a film today. Those that do get made are the rare exception, not the rule. Heck, TWOK, which is considered the classic of the Trek films, would be considered too slow by today's standards. Sure, there are a couple of great battles, but those are separated by lots of character development and some very talky scenes.
Even pure action movies have changed. I think back to James Cameron's Aliens
. An action movie through and through, but what happens for the first 60 minutes action-wise? Absolutely nothing. The film takes the time to gradually build the tension, ratcheting it up bit by bit by bit. Which makes it all the more effective when the action takes off and the last half of the film is nonstop. But today, we need a big 'splosion within the first five minutes, or the film is plodding.