Dude, you have NO idea what a long post can really be, do not worry, this is a great first post!
The idea of a ranking system needs to be improved in 3 ways:
-It needs another purpose: Many people used the ranking system as a way to tell what kind of player you were. But truth be told, I'd played plenty of great maps as a single skull and never moved past that, it wasn't because I was bad, it was because I was constantly lagged out, quit on, and I played turned every so often. The ranking system's only point was so some douche In a lobby could sit there and be like "Uh... I only play with legit knives and up, soooo.... yeah. sorry kid (Leaves)". They need to incorporate another reason for ranks. Unlocked weapons, or clothes for custom characters... Something like that.
-It needs to be map-specific: Just because a player is great at buried, does not show their skill in Origins. This wasn't an issue before because lobby leader-boards were map-specific. I can get to round 50 in buried easy, but in tranzit, nuke town, or Origins it's a different, much more interesting, story.
-It needs to work different. I propose a split way system of ranking up, it starts off with specific objectives for a map that progressively get harder. For example, Die rise: In die rise, fall to your death. ---> In die rise, acquire 10 kills using the selquifier, ---> Finally ending with: In die rise: Complete the achievement: High maintenance: Be the architect of their design. Once this objective is complete the player gains the rank of a skull. The skull is personallized: If they play the map often it gains a zombified glow, if they get to a higher round often, It gets a massive bullet hole in it's head. If they revive players enough they get a syringe background, ect. ect. This way ranking up can be done by anyone with enough skill to get a desirable rank, but likewise they are also given the option to continue to be a better player to constantly give them an even better rank for the map.