Btw, having many ongoing matches, and letting players join mid-match, would place them on the correct balanced match.

No need to break the balance, unless the player wants to not lose time on queue.

While a low rank player could chose higher rank matches, he would get a warning saying “that match is not suited for you, continue anyway?”
A higher skilled player would not be able to pester newbies, unless you implement a higher tier debuff.
So highly skilled players could be limited to low quality guns, movement hindering, low healing items, so then it would be a challenge for them VS newcomers that can use top quality equipment for that tier.