Regarding psytrance and (black) metal being compared to one another, I think this is perfectly valid. In my opinion, similarities regarding the actual music, the atmospherics conveyed in the music and the aesthetics. One of the drawing factors for me getting into psytrance was the 16th note kick and bass - there is a definite similarity to be found in the psytrance k&b and the double pedal kick drum in metal, as well as quite a few general rhythmic similarities. I also find similarities in the atmospheres of forest trance and a lot of black metal - the emphasis on similar aesthetics such as forests and trolls really helps, as well as the main geographical features of both styles (Scandinavia). I can hear this in the music, though, and others have agreed with me in the past.
This is a difficult one. Sure, the kick isn't fat distorted like it is in speedcore, but I do believe that psytrance can be hard music - just in a different way to how hard is usually defined in electronic music (fat, distorted kick drum). For example, I find this track by Sator Arepo to be very hard.
I think the word 'intense' is a better adjective to describe more extreme styles of psytrance. The music can be very overwhelming due to all of the layers combined with the heavy low end prominent in dark psy. I don't experience this overwhelming feeling with any other style of music, to be honest. It encompasses my whole body and mind. Very hard to describe, but I certainly don't experience this with any other form of electronic music.