Ahh you may have played earlier than I did. Most of my playtime was around rise of the walkers. I think I started playing a couple months before the nano machine heal gun things.
I liked being able to pull higher tier stuff into lower tier games, and even grinding up the ladder before I was T10 it was pretty rare for it to feel super unfair.
Yeah, I can totally see how matchmaking for 10 tiers would implode. It really requires a ton of new players or each tier to be unique enough to go back to