I dont think people underestimate the difficulty. It's just on a different scale of difficulty compared to other mods, at the same time it is personal opinion too. There has to be someone out there who can just sightread FL and finds it easy, people are different. "Skill" is just a silly subject because people are good at certain things and find them respectable. Its all matter of opinion, what YOU find impressive and skillful. Personally, memorization doesnt reflect on your taiko skills, it just means you have good memory. I take Pheon's score on that silly song I can't remember the name of, that map is pretty damn hard and he FC'd with hdfl. I find the fact he got an FC more respectable than the mod, because he actually has the playing level to FC. All the memorization is phycological. Same goes for any mod really. Dt, you can play a map fast, cool. Can you perform well? Hr, ok the scroll is a little faster and the acc is a bit strict, cool. Can you perform well? Etc etc.
Just how I see it though. :p