Personally, I greatly prefer to have the options offered by the silenced, scoped, shorty 223 AR and .22lr unit. over just a silenced, scoped .22lr. The 223 can snipe effectively to 1/4 mile, it can reliably take deer to 30-30 distances and a single hit with it (pretty much anywhere, with a softpoint) is devastating to an attacker. 1-2 buckshot pellet hits are not.
One chooses a shotgun out of ignorance and inability with the rifle, and unwillingness/inability to make/acquire a silencer. Along with willful blindness about the probability of the enemy noticing that all you have is a dumbass shotgun, and just opening up the range, enough to render your shotgun essentially worthless (ie, 25 yds, if using cover, or with a helmet, head on prone, 30 yds. That is very short range, and very stupid of you to "think" that all your fighting will be done at such range.
Yes, there's a $2000 silencer for a shotgun, but it aint quiet, especially not with normal (supersonic) 12 ga loads. With subsonic (ie, 400 fps slower) loads, birdshot is VERY limited in effective range on game and birds (ie, 20 yds) This silencer is huge and heavy, so, basically, it ruins the fast-handling qualities of the shotgun.
Shotgun sights and trigger pulls are bad jokes. The safeties don't actually block the sear or hammer, either. Slugs cost $1 per shot, so nobody's really skilled with them. Therefore, using slugs does NOT extend the range of the shotgun nearly as much as people "think" that they do. With just a bead sight, the slugs MIGHT be ok to 40 yds or so, on fully-expose men, not on cover-users. With rifle sights, slugs can reach maybe to 80 yds, which range is still a fairly easy snapshot on the head with a silenced .22. But if the enemy is using cover, the slugs are far less able to extend your range, maybe 50 yds with rifle sights.
The shotgun gives you no option to quietly remove a sentry, guard dog, scout, etc, which the silenced .22 CAN handle. So, fans of the shotgun are just deluding themselves about its "versatility".
kPlastic shotshells collapse if left stored in an extended magazine. That's why Army buckshot comes in solid brass cases. The pie crimp lets in moisture, so you have to one by one seal each rd that you keep ready for use. To be fair, the same is true of .22lr rds, and it's harder to do with the .22's, too.
The huge size and heavy weight of the 12 ga shells just precludes your having enough slugs and buck for much of a fight. If you only intend to be out hunting for a day, maybe you'll only bother to carry 8-10 rds of birdshot. but if you had a rifle for would you be happy with just 50 rds? Of course you wouldn't, eh? You'd insist on at least 100 rds. well, 100 rds of buck and slugs is 11 lbs! So no, you aint talking about having that many shotgun shells. Yet, if the enemy has cover and is more than 25 yds away, what you have, (because you have to use slugs) is VERY poor capability as a "rifle". Because you want buckshot for the ranges you THINK the fight will be restricted-to, you wont have even 50 rds of slugs. So, WHEN, not if, the fight is at such longer ranges, you quickly run out of slugs. Also, your continuity of fire sucks, having to SLOWLY reload a tubular mag every 7-8 shots. Try that with gloves on, in the dark, in the rain, in the mud/snow while prone, some time, or with one hand disabled. Platt put up a very good fight with just one arm and a Mini-14, eh? If all he'd had was a pump gun, he'd have accomplished almost nothing, which is all that mirules accomplished with his shotgun, until the bled out, unarmed robbers let Mirules (who'd been hit in the shoulder with a 223 ball rd) stagger up and execute them, at 3-6 ft of range
3) 30 rd mags of 223 weigh 3 lbs, loaded and ready. the .22 unit is 3/4 lb and 25 rds of the subsonic Aquila 22 ammo weighs 1/4 lb. Since you are saving 6 lbs on ammo weight and if you like, 3 lbs of silenced carbon fiber AR vs the 12 ga, you have the ability to also have armor, night vision, etc, for the same carry load.
the shotgun can't do the job of eithe the pistol or the rifle, so it's just an additional expense and time waster. it can't be concealed or used with just hand hand, and it can't reach out like the rifleman can. So why bother with it?