Most of Death Guard heavy firepower is Plagueburst Crawlers, in my experience. Death Guard certainly reserves the heaviest weapons for the heaviest units.
Looking back at previous editions, the new Death Guard is missing vital fire support (things like Havocs, Obliterators - and anything that had a decent speed). But there's nothing to stop you from plonking down a CSM detachment to bring some of those back in and still paint them as Death Guard - even if you can't run them with DG rules like Inexorable Advance.
Alternatively, if you want to stick with an infantry horde it's probably time to ally in some Traitor Guard.
Ask not the Eldar a question, for they will give you three answers; all of which are true and horrifying to know.