Heroes of the Storm or DotA 2 are fair MOBAs…
… where loss streaks of 15+ happen. Six is a baby streak. My record is 16, but every season I score 12+ once or twice. Usually a similar win streak, too, my best is equally 16.
When MMR works well, your chance to win is 50%. Your skill is equal to that of your opponent, therefore your win chance is exactly a dice roll. Not skill, not performance, not trying even harder after six coffees (which is then your baseline), but pure random.
(Mind game. You are fighting yourself. Who wins?)
MMR is not supposed to swing either, or it would be essentially random matchmaking. Just play it through, at the end of a platinum match winner get diamond, losers get gold, then they get mixed with other players, the match is already a rainbow, but it gets worse.
Of course if you rack up a lot (20, 50, 100) losses, even at balance, you probably either deserve help from the system in the form of easier matches either to give you some free wins or get moved to a proper rank.
And then you have smurfs and other types of climbing people.
As for losing rating at 3:3, the MMR difference is supposed to guesstimate your win chance. In Heroes, it was expressed as a malus (adjustment; you gain 180 but lose 220 points). If you don’t deliver, you just drop and the system stops being expectant.
Too many people think about MMR as a ladder. It’s not.