I have 3 accounts (don’t ask). Each one, placed +/- 100sr from where ever I left it last season. So basically, they don’t matter. Both my trio partners didn’t believe me but the exact same thing happened to both of them. It’s like this with all competitive game modes in OW (roleque/openque/arcade).
Basically, just do your placements and don’t sweat it. Honestly, I usually see tanks gaining more sr than the other roles. (usually see around +/-100sr from where they left it last season, +/-50sr for dps, and +/-10sr for support - all assuming you personally tried your best to get the win). But if that still doesn’t comfort you, then just duo/trio que. I usually see the best results when I trio with my tank/dps buddies while I support so there’s someone who can “carry” in every role.