I agree retopo is always necessary, but that's still far less work than manual modeling from scratch. (Manual modeling may include some retopo steps as well e.g. for different LODs)
The cloth issue can usually be handled during retopo es well, but the modeller needs experience and final technical details should be known upfront, e.g. one or multiple wrinkle maps, full cloth simulation for some pieces etc.
Depends on the requirements. A low detail human model for a game with a camera set further away can be sculpted at break neck speed. I am talking about single digit hours here. Maybe takes the same time as scanning a human and clean up the result. Maybe even less, if you need multiple takes for the scan. And you certainly need no reallife model or expensive hardware for that.
This character took me 6 hours to finish the sculpt... yes, its kinda "low-fi" for an isometric view, but I am nowhere near a professional artist. I would bet an artist could churn out something of that quality in half the time if needed:
How long will a single session of scanning take, especially if you also want to drape the clothing correctly? 1 Hour? 2 Hours? How long does postprocessing take? Will you be able to use the scanned result directly, or do you need to sculpt adjustments to it?
A more complex sculpt for a character model usable for close ups will of course take far longer. Here a scan can certainly help.... though at that point I doubt you want to work with scanned clothing. That will not give you a clothing model that is flexible and animatable enough for the use case. A handcrafted clothing model from a tool like "marvellous designer", and physics driven animation will work better here.
So I am questioning a little bit what is the use case for this scanning project.