There's loads of abstractions that need to be made, too. I mean, if the gals are making the platemail out of plasteel sheets, then it kinda makes sense for it to take so long, while making power armor can be considered mostly just connecting and assembling salvaged power armor parts with armor plating and an helerium battery.
For example, you could consider that, in the making of smartguns, the runts are only pretty much hooking up a slightly stripped down AMG to parts of a slave AI and gyroscopes, then telling the AI to "aim the gun at the softy enemy bits pls", which it does with zero programming because, well, its an AI.
Cars and tanks also prob dont take terribly long because the runts are just assembling premade parts into a chassis, then hooking up some weapon or another to it using pre-built components, instead of making everything from the ground up.
With the boarding guns, maybe the gals are actualy handcrafting every single part because boarding guns aren't commercialy avaliable, they're all hand made, and making stuff out of nothing but basic materials takes a while, regardless of how simple it is.
That said, I also do think the production times do need balancing. Board guns and reaper rifles could def take less time to make.
