All it does is slow down the matchmaking system. It’s slow enough.
A game without skill-based matchmaking is practically inviting players to quit in huge numbers, and to prevent anyone new from ever coming into the franchise ever again. And I’m a little puzzled as to what you consider “slow.” Halo 4, even with the low population, has one of the highest-functioning matchmaking systems of any Halo game ever, IMO. I still play almost every day and I never wait more than a minute or two for a match. What playlist(s) are you waiting in?
That’s probably not related at all to ranking. I play with people from SR1 to SR130. It’s still faster than Reach matchmaking.
above poster ^, SR1-130 ranking has nothing to do with matchmaking skill ranking. The OP is referring to CSR ranking, which is invisible ingame but viewable on the waypoint app or here at QuickCSR.com
And on topic, I disagree OP. Halo 4 actually has a pretty damn good ranking system, the only flaw being that it’s too loose. If the population were doubled or tripled, I’d even like to see it tightened so you never match anyone more than 5-8CSR above or below you. The only time matchmaking is at all slow is late at night on weeknights, and even then I don’t mind dropping out of OBJ, Action Sack, and Rumble Pit and switching to BTB or SWAT.