It honestly helps knowing I’m not alone in feeling like that.
Ratings in games like these are a great example of what is known as the Hedonic Treadmill:
https://en.wikipedia.org/wiki/Hedonic_treadmill
Players want to improve. People want to improve. One's happiness or level of content often is not a representation of their current standing, but moreso a representation at the rate at which they are improving their standing.
Players stuck at 1M strive to hit 2. Players stuck at 2M strive to hit 3. Players stuck at any rating where they aren't seeing steady improvement tend to get dissatisfied with their status, regardless of the actual rating involved.
Even at a tournaments, players who are failing to see improvement get very frustrated, tell themselves they suck, berate themselves, and ultimately start hating the very game they used to love all over getting stuck on the Hedonic Treadmill. The fact is, even a player who is in the upper 99th percentile of smashers will feel exactly like you do right now. They feel stuck, like they can't get better, and that they aren't seeing improvements.
It really is a tough, psychological situation.
It's also why it's so important to make sure you're playing for the right reasons. Improvement will come with practice, regardless of the individual, as long as they're taking active steps to identify their shortcomings and work on their mistakes. The biggest thing of importance is to try to have fun and avoid what triggers you.
For me, it's dropping rating, so I try my best to shut that part of the experience out and just enjoy trying to beat a tough opponent, even if I'm 0 and 5.