Big difference in concussion and muzzle flash if you gotta discharge inside your living room.  IDK, people aren't hard to kill @ 10 paces

Sorry if I cannot be concise. But it goes like this.

In a blowback AR9 (like Colt), the bolt thrust exerted by the brass onto the bolt's breechface, and is almost fully grounded by the mass of the bolt. Less than 1% of it goes on the spring, which applies to the end of the buffer tube.

In either the Scheel or Maxim buffer, between 50% and 70% of the bolt thrust is grounded by the delay mechanism, through rollers or balls. That is the force that applies to the buffer tube. The rest is taken up by the mass of the bolt (note that Maxim requires the extra weight be removed from the tail of the bolt).

Please don't feel patronized, but I know from experience that many people do not realize that the recoil spring does basically nothing. You can remove the spring, load the cartridge, close the bolt and fire that AR9, and it will be completely safe from cartridge explosion. Sure, the bolt will fly back like a hammer blow and land on the buffer. But it acquires that velocity in less than 0.040" of travel.

Assuming that the 9mm cartridge develops 35,000 pounds per square inch, and the inside diameter of 9mm brass is 0.355", for 0.126 square inch area, the peak force is 4410 lbs. But the recoil spring is 20 lbs per inch at most. When it's pre-compressed by a couple of issues, 40 lbs is the force that the spring applies to the bottom of the buffer tube. That is 100 times smaller than the bolt thrust. Only 1% of force keeping the bolt of AR9 closed is supplied by the spring.

I'm understanding what you're saying, but ultimately all that force in both systems is applied as a rotating force on the lower buffer tube boss, which is the weakest part in the system unless you're using plastic buffer tubes.    Even in the Maxim system, I suspect the mass of the bolt is still more than that of the Marlin Camp 9, which has managed to run rather reliably for nearly 3 decades now.

Probably not an ideal system to drop into your cheap plastic lower w/ nothing but a carbine stock, but 7075 lowers would seem to tolerate it quite well.

The peak rotational force the Colt applies to the buffer tube boss of the lower is when the bolt slams into the buffer and the buffer tip compresses against the back of the buffer tube.  I don't see how that force is somehow much less than that of the Maxim.

I am on my second Colt 6951.  Sold the first one in a moment of insanity due to the cash offer.  

I find the Colt reliable with Colt and metalform mags.  Not so much with the Brownell version which I “think” is a metalform  mag as well.

Tried the Ruger PCC with the aluminum hand guard.  But thought it was heavy and poorly balanced.

The Colt is a cheap AR training platform.

YMMV.  Lots of options out there.

IF you enjoy or prefer that, by all means.  By my own perspective, if the desire is for in-home usage, a handgun has basically the same power level, and only requires one-hand to use, and is sufficiently accurate and holds sufficient rounds, to do the job for a close-confines personal home sized spacing.  They make 33 round pistol magazines, if high round count is the desire.  I personally fail to see the benefit of a 2-hand system delivering pistol power in a home confine setting, and do see detriment.  The SMG size platform has benefit for controlling full-auto fire or for usage in a spectrum that is more typical 25 yard distance and even out to 200 yard usage being possible, and in mixed outdoor/indoor settings.  But otherwise, I personally don't see the point as an actual defensive weapon platform, if the concern and requirement is just for in-home settings.  IF the desire is for fun range gun without the loud blast etc, but beyond being a .22; then there you go- nothing wrong with that too.

By all means, it's still effective.  

FWIW, There was the unfortunate video from a year or so ago in TX where a guy killed a frustrated ex-husband with a 16" 9mm.   it certainly can do the job.  Frankly, that whole encounter was a disaster shit-show, but in terms of the tactical setting, the home "defender" exited the interior of his home and CQB engaged an assailant he was chest bumping about on his front porch, in the encounter.  THe handling and manipulation was awkward, and if that assaulant actually was set on a physical attack encounter, probably could have wrestled such a long firearm, moreso than if the guy just was using a handgun.  Point being, I think he would have been better served with a pistol, and only won because the other guys was a ex-husband loosing his shit beating on the door; more than actually looking for a fight an focusing on killing anyone.  Eh, armchairing, others will interpret the setting different, but that was my own takeaway.  BTW, once again, the entire encounter was over in one (1) shot, with 29 extra shots being cumbersome extra's that made the whole system unneededly cumbersome and bulky.