Having spent the slim majority of nearly 6000 matches in the old system, I attest that MM is the best thing that happened to the game since my arrival in Feb 2014. When it first came out it had many serious issues, all of which have been fixed. I am skeptical about how it places people in matches based on MMR, but it's an excellent system that fixed the #1 problem for new players in lobbies: wait time. MM is not perfect and is not designed for handling low player count, but it's what the game needed.
I may be biased because at the same time the best thing ever was added: recommended loadouts. Gone are the days when you have to delay the match forever until trolls bring the loadout or leave. It was extremely frustrating for the whole lobby and it happened alarmingly frequently. Leaving the captain slot and finding another lobby wasn't an answer because a captain slot in a good lobby was gold. It was such a problem that it was better to play with scrubs who ready up before anyone could join. Don't even mention random players joining mid match...another thing MM fixed. For a long period I played AI only ships and had a 43 match winstreak in an AI squid.
Pub stomps were always a thing, and there used to be non swap lobbies which were perpetual stomps. At the beginning of MM the multiple crew form was a big problem, but that is fixed. MM is much more balanced besides the dubious way it sometimes seems to place players in lobbies, and that rematch isn't default. It's efficient and I love it, there's no doubt it was the right step. Don't ban novices from regular matches, they're often a pleasure to play with and people respond well to good communication. 1/3 of my friends list were novice.
PS the custom game menu is awesome. Use it and MM is optional.