[2019] An average Ranked match:

-4v5 if I'm lucky

Is this because someone leaves during the match? Or is it a 4v5 before you even load into the match?

one useless toxic teammate with 0 kills and 4 deaths who does literally nothing other than spamming "gg noob team"
-another useless teammate with 0 kills and 4 teamkilling the useless toxic teammate for being toxic and only making things worse

You should be reporting these players with the in-game Griefing button. I apologize for the overall negative experience with Ranked. I have made note of the recent increase in reports of leavers, especially within Ranked matches.

It often happened to me that matches started as 4v5, literally from the very first second

Did you previously cancel matchmaking before this match?
If a player cancels the ranked queue at the moment the blue bar appears, the match will start without a full lobby it seems.