Old crossbows you have to crank, it takes a while.
As for modern ones, it takes about the same amount of time, maybe little faster.
Those you do not have to crank, which are faster, are also weaker. So maybe... a crossbow you pull for faster intervals between bolts fired but less damage, and one you have to crank for more damage but slower intervals between bolts fired. So the first one the bolt can be dipped in poison and shot from the dark, the base damage won't be too much but the poison will do the work. The other crossbow you can get more "boom, headshot"-moments from. And then there could be the ultimate custom made self-cranking crossbow, that with the power of a fission battery and some engine would crank it much faster than by hand. And if the engine is strong enough it could pull a stronger string, until it goes to the extreme like my idea I linked to!
Truly a heavy crossbow, firing bolts made out of rebar, powered by a fission-powered lawn mower engine hehehehe