Oh, it feels much better! Now that I've played with both, I'm certain that was the issue.
Coming back to try the new control scheme also made me realize that the roll ability actually makes you invulnerable for a short time, which makes the Triangle's spiral bullet attack make a lot more sense. I did manage to beat it the first time without knowing that, though, and I'm just a little bit proud of that, haha.
I think a lot of indie devs let the size of more mainstream games intimidate them, and I fully understand, but games like this are proof that sometimes all you need is uncomplicated fun. I can see myself coming back to play this quite a bit in the future, actually.
Kudos!