It would be easy if it weren't for the bugs, they're responsible for quite a few ended games. Finishing SN without deaths is relatively simple, especially if you've played before, the bugs make it very difficult to recover if something bad happens.
I lost my hardcore world to a glitch. I drove the cyclops into a wreck that hadn’t rendered. It rendered with the cyclops clipped into it. I exited to nudge it about but it came out at terminal velocity killing me.😭
The first time I ever beat subnautica was in hardcore mode. Not very difficult as long as you’re smart. Scariest parts are diving in wrecks and you almost run out of oxygen