Can assure that my pc is certainly not too slow.
Could maybe be because I've been playing on browser rather than from download?
The timing is definitely off on a lot of the songs though.  Some aren't as bad.  Evox Machine (for Gyros)  seems to not be off as much for example.  Don't just take my word for it though.  Would be good to get other input.

And yeah, skill issue.  The songs are very doable with practice (if you ignore the music), but anything past around difficulty rating 7 is just not possible on fast, ultra fast, or insane unless you went to the trouble of making a macro.

Still, loving the game.  For a lewd game, it's clear this has been a labour of love. 
The different storylines and branching options.  The different minigames, and satirical commentary.  And the general vibe is just really sweet.