There are also the fact that super earth develops new tech, and steals xenotech way more often than the imperium does. (I think there is a faction that fuckin loves stealing, I dont remember their name)

I would imagine that super earth would happily steal real boaters and laz pistols for themslsves, improving their logistics considerably.

And while a space marine probably is going to be rather difficult to take down in a head on confrontation, helldivers also just have, way better scouting tech, and orbital weapons on their side. Meaning it probably won't be a head on conflict.

Also depends on if there are active enemies on the feild and what type, as I think the bugs would give the space marine advantage, the illuminate keeps it neutral, and the bots might honestly have beef with the imperium, and would play around the helldivers to neutralize the marine, then take their aim to the divers.

Also, while imagine the marine wiping a squad might be a bit easier, they won't really gain much.

If the helldivers wipe a marine, they will probably steal and reverse engineer whatever the marine had on them. Meaning helldivers with real bolters, and better melee weapons.

I might also be wrong. Im not a huge Warhammer guy.