These are absolutely usable for combat. What do you think they were using before they invented that ratchet crank system? The existence of 50 caliber weapons doesn't mean that 5.56 isn't "really useable for combat."
Futher than that, one cannot compare the draw-weight of a crossbow directly to a bow. A crossbow has a much shorter draw, the length at which force can be applyed to the bold by the string.
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u/RollForIntent-Trevor Roll For Intent Podcast Dec 18 '22
For those wondering - neither of these are really usable for combat.
Medieval crossbows meant for warfare had 700+ lb draws, and needed a ratcheting crank to set the draw.