I completely agree with all of your critiques and suggestions.
After the frenzy dust of the jam settled I looked back and now I kinda think I made some design sacrifices for the sake of aligning with the theme that I probably shouldn't have.
The post jam version is very unlikely to have locked door deaths (for the reasons you laid out and also because i think the hurts the exploration to not walk through the door you just unlocked and see where it leads for yourself) and I was also talking about the design with a dev friend of mine yesterday and we came to a very similar conclusion about the placement of the hearts.
I really appreciate the time and thought you put into this, and am super glad you enjoyed your time with it :)