FastForce

Training Slayer is pretty efficient. You get to use black mask and train several skills at once, though most tasks aren't too AFKable which you seem to like.

There's still a ton of stuff to do and will take you a while before you get bored. Besides maxing out, doing minigames like Castle Wars, reliving all the amazing quests, monster hunting KQ Barrows DKs etc. The OSR community is amazing and the social aspect alone makes it worth it for me. I stopped playing because of all the terrible updates a few years ago and being a very old RS player, OSR was exactly what I wanted to play even if I had to start fresh again. (I also have no idea what EoC is like because I never tried it so maybe I'm biased :P )