Honestly it can be lightning fast or a painful slog. One season I played like absolute trash and went from 3700 to 3000 and I’ve been climbing back up 20sr at a time ever since. Meanwhile one of my alt accounts placed 3800 and it’s been getting 50-65sr per win. 
tho it’s scary to play on that account because of how high sr the lobbies are getting 
I’m probably in the minority here but I think solo queuing is actually one of the best ways to rank up if you’re already near the rank you “belong” in & want to improve, that is. The problem is that you really have to know what to look for in your gameplay. One thing that really sucks about trying to git gud at OW is it’s not very clear what you need to git gud at. Unless you submit a replay or vod to a coach it’s reeeaaal easy to look at all of the feedback the game gives you and think “yep, I’m doing fine, it’s just rng”