Doable pubbie difficulty for the diggers seems to be D8. It's not a D10 fuckfest but it's not a D6 snooze. Pubbies are retards so you have to be able to handle yourself and solo the hordes if need-be. Easier said than done, but my tryhard load out has been
>Heavy Dune armor
>Plasma Punisher
>Ultimatum
>Frag Grenades
>Quasar
>Gun Dog
>Emancipator
>Eagle strafe if outside mission, EAT Napalm if inside mission
Gun Dog + PP let's you simultaneously surface and kill diggers at the same time. Frag Grenades eat condensed groups of bugs alive so you can easily get 10+ kills per frag in a cave of concentrated bugs. 5 nades also helps in hole closing duty. Queso is good enough to handle chargers and the occasional titan while also maybe getting lucky on the bile dragons. If it's an outside mission I may forego the gun dog and bring a RR because there's going to be a bajillion dragons. Emancipator is a panic button/cave objective solver, and Eagle Strafe is just too good out in the open, while disposable napalm is probably the best option to cut off a tunnel from chaff overrunning you. Keep spamming PP for diggers and you have a contained swarm.

Diggers have forced me to become a metafag.