I wrote about this while ago. The devs used to have a bit more progression built in, in that they artificially started you lower after placements so you could climb. This was about as artificial as you can get, even though I normally hate calling anything in a video game artificial since it’s all artificial.
There really isn’t progression in OW and I really don’t think it was ever intended. Not that you can’t improve, but it takes massive amounts of improvement, as you noticed, to do so.
I hear people say that it’s marketed otherwise, but I never saw the marketing where it said you’ll get more SR on time played. I could have missed it, or likely just interpreted it differently though.
Like, BT is taking above about “grinding skill”. That’s just not how skill works. No amount of grinding will raise your SR.