That was my suspicion when I first deleted my account, when it felt the output got worse in ChatGPT and I found highly suspicious when I saw an errand davinci model keyword in the chatgpt url.
Now I'm feeling similarly with their image generation (which is the only reason I created a paid account two months ago, and the output looks more generic by default).
Are you able to quantify how quickly your perception gets skewed by how long you use the models?
I can't quantity it for my past experience, that was more than a year ago, and I wasn't using ChatGPT daily at the time either.
This time around it felt pretty stark. I used ChatGPT to create at most 20 different image compositions. And after a couple of good ones at first, it felt worse after. One thing I've noticed recently is that when working on vector art compositions, the results start more simplistic, and often enough look like clipart thrown together. This wasn't my experience first time around. Might be temperature tweaks, or changes in their prompt that lead to this effect. Might be some random seed data they use, who knows.