You said this before almost word for word and I meant to comment on it then, but why is a visual ranking so necessary for you? It would practically do the same exact thing; it would only be different in that there was a nice number for easy, albeit truncated, comparison.
Firstly, the ranking system in Reach isn't just hidden, it's shit. I matched up before with one of my friends who I was actually in party chat with, completely randomly. Now, not blowing my own trumpet but I'm obscenely better than he is, yet we just matched each other. In Halo 2 or 3 this would not happen, because he'd be floating around the 30 mark and I'd be scratching 45 and above.
Now that's the first thing out of the way, but a visual ranking system also gives method to how you're matching up with people, which as a result reduces the frustration when you have an obscenely poor player on your team. In previous Halo games I could sort of judge that, indeed, a player was just having an off game and that they weren't entirely terrible, whereas in Reach and potentially Halo 4 if it's similarly vague you have no way of telling whether your teammates and opponents are around your skill level. Such as my aforementioned example regarding my friend.
Finally it offers some actual incentive to play on, or have that extra game. If you come on and drop a level then you're less likely to go off, because you don't want to end the evening at a loss. It's sort of like gambling, you aim to increase your winnings so to speak. Right now the game just doesn't have that; it has a generic, boring and entirely unoriginal experience system that rewards play time rather than player ability.