These things make ranked unfair and can be easily fixed

-Team players facing solo players. There is a easy solution to this, which games like VALORANT do:

Match team players exclusively against other team players and disable duo queue above a certain rank. (in VALORANT, since 5 players can be in a team, they disable trio queue above a certain rank.) Example:

Bronze 1 - Legendary 3: All queues available. Teams can get matched against solos

Masters 1 and above: Solo and full team queue, with teams being matched against other teams exclusively

-Arbitrary elo BOOSTS or elo PENALTIES (in lower and higher ranks respectively)

Solution: Base elo gain/loss exclusively on the ranks of yourself, your teammates and your enemies. If all ranks are the same, you should gain what you lose. This can be disregarded in bronze, silver etc. to ease new players into ranked, but not too much beacuse that leads to rank inflation.