I played on a private server without the dungeon finder and honestly it wasn't as great as everyone thought.
First of all, while leveling, people will rarely do any dungeons besides the really convenient ones. Leveling is much faster in wrath and thus you would see less people doing dungeons compared to classic, because it's more of a waste of time to assemble the group, gather all the quests you need and then travel to the dungeon. In Wrath, people just cba to do that for the most part unlike in classic where the game overall is really slow. With LFD enabled you can queue for dungeons while questing and you'll get to play through many more dungeons, so overall you have more variety in content while leveling and it's just much more fun overall.
In endgame, LFD isn't that important/useful though, but it still is a huge QoL boost as you can do other stuff in the meantime.
IMO the big downside with LFD wasn't actually LFD itself, but it was the crossrealm grouping, like you would be grouped together with players from different realms.
So yeah I am generally PRO LFD at least for leveling. If they disabled crossrealm grouping or disabled it altogether for heroic dungeons then I would welcome that. However overall I am sure that in the long run, the lack of LFD would annoy more people.