Yes, your assumptions are correct that I made it a lot easier with considerations for the jam. The controls were meant to feel a bit awkward in revenge mode, which ended up making it a bit too difficult. I did some subtle trickery to make it easier by increasing the hitboxes and adding a little aim assist as well, without compromising the weird, jet-pack-like controls. The difficulty does slowly scale as you play, but it's very gradual that it would be hard to realise. So I think entering revenge mode becomes a riskier strategy as you advance. But because of the lack of enemy types and maybe special boss-like phases, it lacks any feeling of progression which would help players realise the game is getting harder.
I really wanted to add a story that plays once at the start of the game about why the character is cursed. The death curse mechanic is a really good base for a little story that could work across different settings. The issue was I didn't want it to be just a paragraph of text, I would want to show image or animate it a bit, which is not something I can currently do very easily or quickly.
I agree about needing some more little indicators. I kept it in the back of my mind during the entire development, but never came up with a solution that I could implement quickly. I think the best method for this problem would be to just try different solutions, like the one you suggested, and just tweak and iterate until finding something that works. Which wasn't going to be feasible within the time constraints.
I really appreciate people like you who show genuine interest in other people's projects and give good suggestions. Thank you so much for your detailed feedback!