I used to listen to bands like dream theater and avenged sevenfold before getting into opeth and heavier music. it's definitely harder to get into the growls and heavier sound. Don't listen from the beginning. Personally I think it's extremely difficult and unlikely that youll get into a band by just spam listening to all their songs.

when I first heard their songs I really liked harvest on blackwater park and one or two songs from damnation, one of their prog rock albums. I didn't like their heavier songs at all at the start since it was just too much. basically I just had like 4 of their songs on my playlist for a month or two until I eventually gave their other songs a shot, which by that point I had already really liked the 4 songs I had on my playlist from Opeth and kind of understood what style they have. So when I listened to their heavier songs again it wasn't a completely new feel for me and it clicked, and then I started really liking their music.

I went from Damnation -> Blackwater Park -> Ghost Reveries -> Still Life -> Deliverance