Personally, I don't really care which is used. Yes, I like 1.8 PvP better but it's probably because I am better at it than 1.16. However, 1.16 PvP makes sense to me with how hades is now. Hades is more aimed towards PvE rather than PvP. If there was 1.8 PvP then beating the hades mobs would be so much easier and less grindy than they are now.
With that being said, If hades were based more towards PvP rather than PvE I could see the PvP being 1.8. However, since it's based more on PvE it makes sense to me as to why it is 1.16 PvP.