It's interesting you pointed out the difficulty spike, I increased it because I thought it was too easy (initially, the 2nd level only had 1 enemy with faster dps). I guess I kinda lost sight of the gentle progression because I was working on it constantly, no wonder I found it easy to play, lol, definitely something I'll be paying attention to next time.
For the enemies moving instantly, it was an intentional decision, I wanted to mimic MMSF's feel of enemy movement. I think it relates to the progression thing, I was actually trying to move the enemy slower, with larger cooldown initially. But it got boring for my brain. Now I kinda realize, it might be the same problem, I was too close to the project. I appreciate the feedback!