I was wondering if maps with a high OD + a large amount of hit circles would give more pp than maps with high OD, but lots of sliders. I know you're taking each skill set into consideration (aim, speed, accuracy), but I feel like high OD maps with much more hit circles than sliders should be favored slightly more over sliderspam maps. Maps with lots of sliders and high BPM should give an aim boost rather than accuracy, especially if the AR is high.
Speaking of high AR's, are they considered in the calculation at all? AR8 and AR10+ definitely deserve some sort of boost. Reading is a skill separate from the others (aim, speed, accuracy) and should be taken into consideration in my opinion, especially on maps that go above AR10 with DT. DTHR is an extremely hard mod combo, and I know that it would probably give a good boost already, but I wondered if it's AR changes affected pp gain in any way.
Also, silmarilen is right. I've played both of those, and though Bloody Night might be harder in terms of jumps, Refrain is harder overall. It has smaller jumps and slightly shorter streams, but it's faster and has higher OD. I always miss at least one note on it, and when I don't, I get shit accuracy. It's much easier to get a good accuracy on Bloody Night.