I believe I made a mistake, I thought I remembered applying a 2-string sweep like in etude VI in the buried alive solo, but after playing it again I realised I actually didn’t. I probably mixed it up with with another song in my mind. But yeah the part you’re talking about seems most easily played with economy picking.
But still, it might be nice to check out some etudes. Sweep picking etude VII actually contains some of the 3-string sweeps of the buried alive solo and it’s basically the same as etude VI but on 3 strings instead of 2.