Out of all the people. After all my work. My little brother got perfect bed adhesion. He figured out the extruder tip was slightly too high, and would drag the extrusion on the build plate instead of smushing it into the texture, so it wasn't binding properly.
He found the solution deep in some ancient reddit post. The reason we hadn't uncovered it earlier was because all of our google searches gave us the simplest answers for "Ender 3 prints not sticking to print bed". The answers were always the same. "Level, check temp, and slow it down." I think something that also contributed was the amount of hate the Ender 3 gets online. Be it joking or serious, it had put us into a sort of defeatist mindset. "Yeah, the printer sucks. That's just how they are."
It's a shame it took us this long, but I'm glad it's working well now.