people who solo que in ranked should get a -5 rp discount

@Cro_PitttDefinitely. Solo lobbies are much much softer than 3-man lobbies.
It's quite typical for half of the teams to die before 1st ring closes in solo lobbies in plat, while 3-man plat lobbies, you'd sometimes be looking at 15+ teams still alive at that time.
I recently was in a solo lobby where the last 6 teams were 5 solo's and 1 full team. Obviously, the full squad won, but if you were 1 of those solo's, you'd have a much better chance to get good points, than if you were in a game with 5 full squads and you. In 3-man lobbies, there's usually mostly full squads still alive at the end.

Best way to rank up is still duo though (assuming you have anyone better than random to duo with), as as far as I've seen, 2+1 still play in solo lobbies, at least most of the time.

P.S. That's most likely not true for master/pred lobbies (maybe even diamond), as there's not enough players to fill separate lobbies for solo/duo and 3-man (and I would guess the preference is to put them together rather than mix players of lower ranks in). But for plat - that's definitely still true (unless you play on a small server with small playerbase? I have no experience with that, I play only EU/NA PC).