I would be way more frustrated after being kicked once to make some space to someones buddy/boost than all the frustration I had from key leavers. I don't get that many tho because I mostly do my keys and I filter people.
There might be a solution to leavers out there, but I don't think any of the mentioned in this thread would work because it must accommodate full pugs, part premades and full premades in a fully player made composition who might have different goals (push/weekly/completion )where you can't tell if someone left/was kicked for valid reason unless you manually review it and actually understand how m+ runs in that context. Being toxic would be easy, but how would you know if someone was griefing by ass pulling/intentionally bad dps/healing/semi-afking/not using skips and so on and when was that intentional?
Lol has intentional feeding report, but I have been reported by full teams for intentional feeding after I was counter-jungling and died. Nothing has ever come from it.