That's an excellent point. Kirk, McCoy, and Spock argued all the time; Kirk teased McCoy and Spock sometimes, but McCoy and Spock gave each other shit and really meant it. There were disagreements about policy and course of action, but in the end, they (usually) came to an agreement and a plan that worked.
With TNG and the others, everything was so civil and polite and politically correct that it got downright boring sometimes. And yeah, too many main cast members, all fighting for screen time. With Voyager, the crew was actually composed of members of warring factions forced to work together, and after half a season, there wasn't even any mention of it, let alone any conflicts within the crew. Blah.
Conflict creates drama, and drama is more interesting than everything shiny and happy all the time.