Thanks for taking the time to write this, I really appreciate the honest feedback! It was definitely frustrating to play before, but I just pushed an update that fixes exactly what you mentioned.
The game is now strictly locked to the real 84x48 resolution, and those unfair hitboxes are completely fixed (dying to thin air was the worst, sorry about that!). The jump input buffer is a brilliant suggestion, adding it to my to-do list right now. Thanks for playing and for the great tips!