Maybe you are getting a lot of dmg. In order to heal you need a full hunger bar. And healing depletes your hunger bar fast.
There's also a hidden second hunger bar. You need higher quality food to fill that one. Maybe you are using lower quality food now.
Checks out with my experience in university. I had like 3-4 classmates in software engineering that could program a simple program that ran. And this was before LLMs. You don't even need to cheat to pass while being absolutely incompetent. Of course, some people also cheated.