Given that Sleep Token is very vocals-driven, maybe that's what you're missing in AdP. Vessel is a fantastic singer (one of the best in the game right now), but I'd say that he's no better a guitar/bass player than Khn. As far as drums go, ii is one of the greatest rock drummers of all time, but Klek is really solid and fits his role in AdP perfectly. Sleep Token is an amazing project, but even those guys might not appeal to you in a different format (since you like heavy music). Have you checked out any Blacklit Canopy? Did Vessel's previous life as a coffeeshop folk singer appeal to you at all, or do you need the volume turned up to get what he's doing? Inversely, have you checked out any La Poêsse? Maybe AdP just isn't hard enough for you, and their previous project would appeal to you more.

Also...do you like electronic music? I'd say that AdP are kind of a mash-up between rock and techno (my call is that they're a mix of Buckethead and Daft Punk, haha) and, if you don't like techno, you might just not appreciate the way they arrange their songs.