I have mulled this question for yrs. And I still haven't seen what I think is a "carbine" in pistol caliber. The problem I have with the AR format is size. It can be stripped but is not light. And I don't see 100 rd mags or belt feed as a requirement.
What I do have is a 1969 circa, Ruger .44 mag Deerstalker Carbine. It looks like and feels like the Ruger 10/22, with more punch. It has a tube feed for 4 rounds, so it is not HI-SPEED. It is only about 5.5 lbs loaded. It handles and shoots well. I took an ammo sock for 30.06 and mounted it on the stock, holds 18 rounds. Mounted an older Aimpoint,, Should get me past the initial charge, until I get back-up.
Net Net,, your requirement for a carbine need definition.
Hi-speed??
Plinking??
Home Protection??
Hunting??
I get all scenarios covered by the Ruger,, until the Zombies come, in which case I have AR, AK, FAL, xxx choices..
Don't forget the AK, med-light, plinker, ammo prices coming down, if you run out, your neighbor probably has a stash of ammo,, so do the Zombies.. It has a real folding stock or no stock in the case of a pistol...
Not saying the .22 AR upper,, (or in pistol cal) doesn't make sense... But ,, I am a cheepo,, 500 USD for 1/2 a gun is border line. My Ruger was less than 400 USD,, currently you can find the older ones for around 500+-
Here is my Ruger, my AK pistol and an example of a custom AK pistol I lust for..