My point being, why 10k for a map that takes a lot more work, and 10k for a weapon that dont.
It's all relative. Just because a map is big doesn't make it much more work. Maps are static, can use existing assets and when you're heavily focused on historical accuracy gameplay becomes emergent from the terrain as it was rather than heavily focused and designed/tweaked chokepoints. Saying that, I don't want to distract from the fact that designing large open maps that still have tight gameplay is an artform it itself - I imagine they'll be working at a loss when developing any of the maps listed as stretch goals.
However, what about making an additional weapon, that functions like no other weapon in the game, do you think isn't a lot of work?
There's many reasons flamethrowers aren't a mainstay of WW2 games in the past and modern games don't feature "futuristic" alternatives.
Off the top of my head at the most basic level you've got:
3rd person model x 2 (Germans and Americans both had them)
3rd person texture x 2
3rd person animations x 2
1st person model x 2
1st person texture x 2
1st person animations x 2
World model (if you can die and drop it) x2
Inventory integration (ammo etc)
Hitbox integration (shoot the fuel tank on their back)
Flame physics and world collision
Flame interaction (what can be set alight? - consider performance vs flexibility vs desirability vs gameplay)
Physics, and textures for setting enemies alight
Death animations for enemies
Death animations for player
Damage radius of flame (again, consider gameplay and testing required)
Gameplay considerations in terms of class/points/cost
That's just their first draft. Once they actually release it to Alpha they'll likely have a tonne of feedback with bugs for them to fix and a tonne of feature requests they'll need to work though, prioritise and implement.
I'm also probably missing stuff - but that's not 1 hour of work. Not one of the things I listed above it its own is 1 hour of work. Most, if not all, would probably involve two people working over two days.
As a genuine offer, if you really think what you're saying, I'd be interested to see something you completed to a standard that you think could hold up to the scrutiny of the online gaming community in one hour, let alone a day.