Let's be very honest - there is way more to improving than just your pure aim and you are tunnel-visioned on the superficial aspects of aim such as HS% and KDA. You don't see or feel improvement because you think you're already improved in what you think is important rather than looking at the bigger picture.
Any professional or high-rank analyst would see how you highlighted on those two stats and probably tell you the same thing that you care about things which don't matter in the grand scheme of the game. Consider your decision making, your map awareness and your communication as well. These qualitative factors which impact your game will be constantly changing and something you will feel like you can always improve upon.
I can understand that this might sound hypocritical in a sense given how many pros and coaches say you can get to ascendant or diamond with aim alone. But they are talking about aim which can carry a team of clueless players and AFKs - if you can't do that then you aren't at the mechanical aim level these people talk about which can get you in the mid-region of the ranked space.
You definitely have a lot more to think about and I think a short break from the game to help reset your mental is well-deserved and perhaps even required to get back into ranked with a better idea of how to climb. I can understand playing without your friends sucks and it's way harder - trust me, I've been there. However, if you can prove to yourself you can climb, they will see your efforts and stack with you.