Except in very limited exceptions an AR -15 carbine does everything better except cost, and the gap in price is smaller than ever.
PLEASE PLEASE PLEASE tell me where to find anything CLOSE to a $300 AR15, even trashed and abused. The cost of a bottom dollar AR15 is right around $600 or so - you can get a beast of a semi-auto shotgun for $600, or a brand new, solid and reliable pump shotgun between $250 and $350 depending on where you go. That looks like a fairly significant price gap to me.
At SD ranges a SG does not offer a pattern large enough to improve hit probability over a single rifle projectile.
You mean there's no improved hit probability between a .70" projectile (or 1-2" spread of buckshot) vs. a .22" projectile? You must have fantastic aim under severe stress (ie, someone breaking into your home at 3am)
Good 223 softpoint ammo is more effective against humans at any range.
Generally if you're shooting humans at range, you're either in the military or will shortly be in jail for murder due to the fact that at further ranges, the threat loses the necessary "Immediacy" that most SYG laws require. At closer (reasonable self defense) ranges, the advantages are nil.
Even good 223 ammo is cheaper for practice than buckshot or slugs
That's one truth, unless you reload, then the difference is significantly less.
An AR has about 5 ft lbs of recoil vs 30+ ft lbs for a shotgun loaded with slugs or buckshot. That is 300 win mag levels.
No argument there - The carbine definitely wins in the lack of recoil department, which increases accuracy for follow up shots.
A carbine is far more compact and lightweight.
That's not a given - my 14.5" barreled AR15 carbine is 2 inches shorter than the shotgun I just recently sold, and it's nearly a full pound heavier than a standard $300 synthetic stocked mossberg 500 pump shotgun. 2 inches isn't much when you're talking long guns.
A 223 softpoint round is less likely to overpenetrate in building materials.
.223 FMJ is less likely to overpenetrate through building materials too - Can't disagree with this one either.
A carbine offers up to 6X more ammo capacity.
I understand the argument, but if you can't do it with 5 or 10 rounds, you should probably run away instead of spraying the area with more bullets.
While you may never need it, a carbine offers much more versatility at longer ranges.
Were we talking strictly about self defense, or are we now including hunting and target shooting too?
The only situation where a SG has an advantage is if fired at ranges over about 10 yards and up to ranges of about 30 yards. Any closer than 10 yards and a carbine or handgun is a better choice, any farther than 30 yards and a carbine is a better choice.
The only situation a handgun would be a better choice than a shotgun OR a carbine is if you can't legally or physically handle a long gun in a given situation (carjacking, out in public in some places, etc)
There is a reason the SG has become obsolete in LE and military use.
Really? Obsolete? The U.S. Army has active contracts for shotguns, and every single LE agency I've ever had any kind of experience with still uses shotguns in many MANY circumstances to this day. Where do you live that cops and soldiers don't use shotguns anymore?
Sorry man - I agree with some of what you said, but you're drinking too much kool aid in my opinion.
Are shotguns extremely versatile? Yes, absolutely.
Are carbines just as versatile? Of course.
Is one better for some jobs than for others? You bet.
Is a carbine automatically better for every situation than a shotgun? Maybe if your mall security job requires you to wear Lv. IV body armor and carry MP5's and long range sniper rifles.