don't worry, you don't lose speed for playing slow maps. I think you shouldn't look down too much on DT, speed is important. your accuracy isn't bad now, I'd say it might be a better priority to try and maintain that accuracy while FCing harder maps.
you should spend about 30% of your time playing hard rock if you want to learn it. Start on easy sub 4 star maps, and basically you just need to keep retrying the same song until you can get full combo's with good accuracy. then move onto another one, etc etc until you start getting better at sight reading HR. Here are a couple of easy HR maps. (you'll need to find ones to practice triples and streams as well though) https://osu.ppy.sh/b/313213?m=0 https://osu.ppy.sh/s/57393
you should spend about 30% of your time playing hard rock if you want to learn it. Start on easy sub 4 star maps, and basically you just need to keep retrying the same song until you can get full combo's with good accuracy. then move onto another one, etc etc until you start getting better at sight reading HR. Here are a couple of easy HR maps. (you'll need to find ones to practice triples and streams as well though) https://osu.ppy.sh/b/313213?m=0 https://osu.ppy.sh/s/57393