It is generally true, but there are various additional considerations related to vacuum and 0-g which makes firing normal guns complicated. Besides, it's simply a design feature - not an ass pull by any means, but a simplification (like firing standard guns underwater is also impossible in XCF).
Sorry, but this is completely out of touch with physical reality. Bullets don't become magical in space.
So are handheld laser and plasma weapons depending on who you ask, because of things like the plasma projectile wanting to decohere and the energy consumption. Yet we accept them because they're common scifi and gameplay staples, and elements that already exist in the game.
Sure, one of the considerations for micrograv/vacuum combat is recoil, so you're probably going to use a lower-velocity round (so lower base damage) or one that can accelerate in-flight (hence gyrojet). It's probably going to be a relatively large and heavy round as well, which would limit capacity (but the UAC guns are largely already low-capacity, so that's covered). All in all, not great at punching through conventional body armour but fine for use in space against targets that are probably going to be quite lightly armoured.
The UAC Pistol embodies most of these already. It uses a high-power round, has fairly average capacity, and a hidden armour effectiveness modifier. The SMG is relatively low capacity for an SMG as well. The Rifle is more of an outlier since its 3shot function means the magsize is effectively 36 (a bit above average) and it has fairly normal damage for ballistics.
I really ought to explain my internal train of thought more sometimes.Iunno, I'm mostly just throwing stuff at the wall to see what sticks. I realize some of it is going to be a little "out there" or more game-vs-reality, but that's just a side-effect of differing design styles and mindsets. The only other stuff I can think of basically requires whole new engine features or extension of existing ones, and this isn't the place to ask for that.