Bedrock combat is just... a mix of both of them, but Java has a very distinct line.
Here's how I would propose to give a purpose to both:
- 1.8 PVP - Competitive games, tournaments - Bedwars, Skywars, UHC, Factions, etc. 1.16 could technically work on the last two since they're far more traditional gamemodes, but 100% not on the first two. Major servers like Hypixel implement workarounds to make 1.16 combat as similar to 1.8 as possible already. These modes are simply too fast paced and way too many combat techniques are impossible in 1.16 combat (combos in the traditional sense, block hitting, w-tapping, etc.)
- 1.16 PVP - Survival. Literally just traditional Minecraft. No competitive play. Modernly the Minecraft combat meta has changed so much to be more survival oriented that it's impossible to adapt for competitive play. Even with workarounds making it like 1.8 PVP, it's just not a fun way to play, unless you're on a survival server with friends where you have the space to actually wait for the delay, or jump to crit, etc.