Yeah, I do think that's a decent way to balance the difficulty, but I can see that balancing a game like this can be pretty difficult! Maybe something like time or score as a secondary factor to the attack speed, in the case of time, as an encouragement to think fast, which would be quite chaotic with another person, or with score, to provide a consistent challenge
And yeah, moving patches could definitely solve the problem, of, well, I guess you could call it camping!
Personally, the difficulty at the start was fine, buuuut as soon as I got an optimal strategy it became less engaging for me and I'd usually only take damage if I cross-wired the controls in my brain which is really just an issue of me playing on my own haha