IMO these are not ‘pistols’...they are CQB SMGs.(non-auto in civilian versions)
Just my opinion...not saying they don’t have a place.
I have one of the KelTec 9mm folding carbines. Right out of the box it shot four inch groups at ten yards. And I bought the Glock mag version so I could use 33 round mags with it. Thing folds up and carries in a book bag!
I agree.
A major problem with using rifle ammo in a pistol is that you waste a lot of powder in muzzle flash. You just do not have enough barrel length to get full burn of your powder load.
You can try to use a faster burning powder but then you end up prematurely eroding your barrel.