I'm glad you like the game despite it being so small, and I hope the upcoming updates live up to your expectations ^-^!
I will most likely nerf the Repulsion Burst spell heavily, along with its Upgrade Cards; the idea is for this spell to be defensive, not a nuclear bomb.
As for the difficulty scaling and the boss, I will be tweaking them a lot in the next update. Honestly, I already have a list and started working on v0.3.0 a couple of days ago bit by bit. However, I don't want to publish anything just yet without being completely sure that I can pull off what I'm currently designing. In fact, it's something so big (for me, personally) that I will most likely split it into two updates to avoid Scope Creep.
Without spoiling too much, I will divide the enemy scaling over time into sections, and I'll modify the Boss's stats (so it's no longer an absurd bullet sponge). For now, the Boss's behavior will remain the same, but in the future, I plan to implement your ideas, like giving it dashes or maybe special attacks.
Thank you so much for your questions :D! It might not look like it, but they also help me rethink things or focus on stuff I might not have given much thought to, haha.