I'm not really that experienced in taiko, so I'll just speak from my perspective, instead of trying to lay down some hard facts.
I read that you guys think HD<HR, but I think the better you get, the easier HD will become, because you sort of memorise the patterns with muscle memory, so you don't need to "think" about it (or at least that's what I noticed). I only recently started playing HD, but I still find HR easier than HD on a map like this
https://osu.ppy.sh/s/45672 , even though I play on 1366x768.
Also I'm a ddkk player, though after seeing what kddk players consider hard, I found that it's similar to what I find hard. Like I think ddkkddkk-- patterns are a breeze, while triplets (especially kat triplets) in a stream is really hard or annoying.