So what gives a guitarist a heavy sound is the lyrics? lol
The lyrics certainly compliment it. A lot. If you notice, Cantrell without Staley isn't quite the same. I would say the bendy thing ( Think What the Hell Have I) and his style along with tuning a half step down as a matter of course helps. I believe a lot of the way Cantrell developed as a guitarist was in direct response to writing music for Layne Staley's demons.
I think comparing Cantrell or AIC to those doom guys is pointless, but I fail to see where music that Cookie Monster sings lead is considered "Heavy". Music wise they were doing all that stuff 25 years ago. It's called thrash.

