I don't know if Glass modifiers were a thing when you made your comment, but they definitely are now. I'm not even good at rhythm games but I SS-ranked everything using only Glass (on normal levels, not endurance). It's pretty forgiving as long as you actually manage to get the circles.
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Wait, your problem was simply trying to BEAT the levels? This game is lenient enough I didn't imagine that could be the issue (and more relevantly, I somehow managed to completely miss reading that in your comment, my bad), but yeah, when it comes to that, you really do just need to be fast enough and maybe roll a few decent (or just effectively null) perks.