Hey there!
Comparing ratings across different platforms can be challenging due to the variations in rating systems. However, I believe that Chess.com has the most players, making the ratings here more accurate. Your improvement from 1500 to 1800 on Chess.com does indicate a significant enhancement in your skills. Even if you feel like you’re still making similar mistakes, it’s likely that other aspects of your game have improved.
Note: I’m not that experienced or good at chess, so my comment may not hold much value. 
Hi, I've read some posts about how Fide rating and chess.com rating compare to each other. Seems like it's somewhat close. Does anyone know about the old yahoo chess ratings? I used to play there and hover at about 1500. This was about two decades ago. I'm about 1800 now. I felt like I've improved from that old score, but I've no idea how yahoo chess compares with this.
My OTB when I still played in school clubs about two decades ago was about 1400 to 1500. No idea if I've gotten better. I still have virtually no openings memorized to even a shallow degree, same as before. And still blunder queens regularly. Any computer opponent at 1600 and above will start wrecking me usually. Again, same as before. So I wonder if there's any merit to my feeling of general improvement.