Congrats on beating story mode!
Making unfair arcade modes is a classic flaw of mine, it should be easy to beat with Sun and Black Hole (they are op), but it's true some girls are a bit too weak.
Memorizing patterns can help a lot, most aren't random so once you find the perfect spot you won't get hit. (Mercury has one attack where you can literally stay still "Nightside Ambush").
The download version is recommended for this mode for loading progress since I couldn't get it to work on browser, but yes, I don't think most people will be completing the challenge with everyone.