I wholeheartedly agree with the title and the first half of your post. That said, there is another big issue with the pre-round system I'll explain below, but I imagine it's not as easy to fix as lowering the player count threshold.
The issue is that when you're in pre-round, free to roam around the map to keep yourself entertained, and the game says "X/8 PLAYERS NEEDED TO START ROUND X/8" you might think it means at least 8 players on each side, in realty the condition is any combination of 16 players on the server, in total. This means the game will break pre-round with 8v8, 9v7, 10v6... or even 16v0.
Why is this a problem? Because once the map has reloaded into ranked, then—and only then—the game actually wants 8 players on either side or more. You could have 16 players in the same team and the game won't do anything about it, other than waiting for more players to join the opposite side. At this point people are forced to stare at the "hangar screen", with the UI saying "Waiting for players to join", which is rather confusing because there are actually enough players on the server, they just need to be balanced between teams.
This design flaw is then exacerbated by additional problems:
To make matters worse, once a server gets to the "hangar screen", there are only two ways out: either enough players join to start the round, or player count drops low enough that the game reverts to pre-round. Problem is that the "too low" threshold is merely 2 players—TWO, versus the 16 needed to start, so far too often servers end up in a vicious cycle where there aren't enough players to start the round (even though there might be if teams were balanced), people get bored of starting at the "hangar screen" so they leave, but since more players trickle in the player count never drops low enough to revert to pre-round, which would allow people to spawn in on the map and make the waiting more bearable. (Exhibit B)
In conclusion, it's painfully obvious that the pre-round system was not designed to work with low player counts. Lowering the players threshold would help a lot but it would only address half the problem.
PS: this is a very minor problem in comparison but on Wake Island and Pacific Storm pre-round (for some modes) the US players are forced to spawn on the carriers, so they've got to swim for literally an entire minute before they can reach land (since there are no vehicles in pre-round). This is far from enjoyable so it wouldn't surprise me if those map have a worse "seed success rate" than the rest. As far as I can tell from looking at the other maps, the pre-round spawns don't have to match the actual HQ spawns, so it seems this could have easily been avoided.
PPS: as far as I know there is actually room for 8 playlists but they deliberately left 1 slot empty, this means that "Rush, Frontlines & Domination" could be brought back without sacrificing anything. That said, I think Domination should be split from Rush and Frontlines (it's a completely different experience) and merging Conquest back into a single playlist (like it used to be originally) would make room for it.
As for merging Conquest, I think the least disruptive solution would be to just stack the entire Strategic playlist at the end/in front of the Tactical playlist, this way "Strategic players" could use the server browser to join the first "Strategic" map and enjoy a full session of their favorite maps, and vice versa for "Tactical players". That said, personally I think I would enjoy it more if the two playlists were much more intertwined, like 2 "Strategic" maps, then 2 "Tactical" maps and repeat, so neither vehicle-main players nor infantry-main players are constantly dominating for the entire session.
PPPS: I'm writing a lot for a game which hasn't even been glanced at by its developers in 5 years. I guess I just needed to vent.
