I have a pp anomaly to report.
I have
https://osu.ppy.sh/b/30275 in my top 10 performances without any mods, but I played
https://osu.ppy.sh/b/212095 with Hidden and it's not in my top 10 performances, despite being much harder than the first example.
Normal

Hard

I checked the new pp star rating for both of these difficulties and the Normal difficulty rates 1.87 compared to the Hard at 1.85. The Hard difficulty is clearly harder, despite the Normal having more clickable objects. The jumps in the Hard are much harder than any pattern in the Normal, so I think one more 100 shouldn't make that much of a difference in two maps that should be considered nearly equal in difficulty (supposedly), and certainly not enough to outweigh a Hidden mod play of it. Anyways the difficulty of the Normal should not be anywhere close to the difficulty in my Hard. It's not difficult to play.
Also I found that
https://osu.ppy.sh/b/10878 play isn't in my top performances as well. I know it's a Normal, but really I'm playing Flashlight with Hardrock for over 3 minutes and I only get 2 100s. I'm really surprised that this hasn't shown up higher. It is my most played song for a reason. This was not easy for me to get this score, mainly because of how awkward the note spacing is.
I think note density is playing too high an importance in these cases. A higher note density does necessarily mean that a map is harder, and the opposite is true for a map will less note density. Also circle size and the smaller hit window when HardRock is applied doesn't seem to make a huge difference when you play with mods that inhibit your ability to be accurate. I'm not sure, I don't usually play with mods in standard.
Longer maps with flashlight should definitely get more of a bonus than shorter maps and the difficulty raises extremely high when you get to harder difficulties. So much so that I wont even bother, but if I want to put the effort to spend 8 hours learning a normal map in Flashlight and FCing it I want to be rewarded. Skill with playing with accuracy reduction mods is more important than maps that just like to give you 100s without mods, because most likely the beat is awkward to follow.