Placement doesn’t matter. You’ll end up in ranks you belong.
Sure that is why its possible to have multiple accounts at different ratings regardless 
It is. While placements do not take wins/losses into account new accounts still have fluid MMR. Meaning if the person in question gets lucky and wins a bunch of games they will increase their SR at a faster rate than they normally would. You’ll notice how most of these different SR account stories played like 20 games, which is far from enough for the system to become certain they are where they belong. It, after all, cant know the person’s other account and what their SR is there.
MMR is only 1/3 of the regulation of an accounts first placements 
Being a bully that make people leave should also be considerated into the SR. For OP it clearly did.