About 3 seasons ago I started getting more and more Diamond/ Masters in my pub games, to the point I was getting discouraged playing pubs. So I hit Plat4 and left it at that every season.
Was just too hard and I wasn't near good enough at the time to not bounce off the demotion protection every other game. I've been stopping at Plat4 since I first achieved it in season 4. Last season first split, pushed hard solo queue into D4. Kinda same boat as you, just not as far along.