I think you should base the ranked mode off of shinobi strikers and my reason why is because that game is a 4v4 objective based fighter with a similar game mode and class system. The rank system they use is a letter grade with each letter having different levels like s1 s2 s3 etc.
The best part of the system they use which I think should be implemented in this game is a performance based system rather then wins and losses, you earn points in game by claiming objectives killing enemies healing allies etc. That then go to giving you a grade for the match, that grade then decides how much points you earn for your rank.The reason this system is perfect is because a player who wins but sits in base doing nothing would score 0 points except for a win bonus thus scoring a D and 0 points. On the other side you could have a player who does everything in his power to win but his partners do nothing so he loses, and even though he doesnt get the win bonus he scores s grade and max points towards his rank.
I was a top ranked player in shinobi strikers for multiple seasons I was number 45th i. The world for a season then 32nd and the last season I played I was 4rth in the world and i did all that while being a solo player. I think that is the best system in a team based game so solo que players arnt punished for not having friends... I'd love to hear your response and opinions because I love this game and have been playing it non stop since you released it, I have ambitions of being a top ranked player In this game so I'd love to help any way I can.