So what exactly is so bad about him using a K98k and a Stielhandgranate?
The K98k was, overall probably one of the best Bolt Action Guns in WW2, and while more modern Bolt Actions (which, lets face it, often share a lot of its design and features) may be better in some areas, they would also take some more materials.
Of course, with all the cheating, you could probably forget about that issue, but still, thats a perfectly reasonable choice.
And the Stielhandgranate, well, you can just throw those a lot further than normal ones. Thougj i do agree he could'be simplified the fuse for the Harpy.
Then again, i don't think he knows much about weapon design so he just thinks of some iconic weapon and the crafting table does the rest. Not much customization options there.