Skill is skill. Shooting is shooting. That's what we say about pistol shooting all the time and why a USPSA GM is regarded as a highly-skilled pistol shooter and not "just a gamer." We have known standards and test by which we measure the skills of a pistol shooter. It may not be 100% perfect, but we have a pretty good idea at this point.
On the long gun side of the house we have some carbine tests and skills, although less than pistol. For closeup speed we have the VTAC 1-5, El Prez, etc. Bill Blowers @ Taprack has some stuff pushing you out to the 25yd line. Beyond that you have Defoor's carbine tests, but things start to get pretty narrow from there. We have "standards" that in my opinion and experience are waaaay too loose. For instance, most will tell you that a 2.5 sec carbine reload is really fast. I have video (unfortunately don't have his permission to post) of a friend doing a 1 reload 1 with a carbine and the reload is 1.3. He's sub 1.5 all day. I think we can and should do better at defining carbine reloads.
So on to the topic at hand: shotgun performance. In both the pistol and carbine realm, we've seen competition lead the way for performance of "tactical" shooters. Rob Leatham, TPC, others being hired by top tier units to teach them how to shoot pistols. The emergence of the LPVO for carbines, offset irons, etc, etc.
However, there seems to be very little competition crossover for shotguns. Just like anything else, there are things done with shotguns in competition that are not viable for a "tactical" or non-competition environment. However, most of it is and is just being ignored. For instance: on a platform where keeping the gun full is the hardest part of running it, why don't we ever hear about shotgun reload times outside of the competition realm? Things like Keith Garcia's "Load 12" drill are absolutely applicable to "tactical" shotgun shooting. (https://www.youtube.com/watch?v=FXslwiq9c8I&t=181s)
We have some real experts in house here too. @P.E. Kelley is a multiple world champion shotgunner. On the tactical side we have @Tom Givens and @jlw doing the rangemaster thing and then @TCinVA has his thing going on too.
I've got 27 minutes left to go in the P&S "The Gauge" modcast and while there are some good nuggets, I'm disappointed in the overall commentary, which seems to be that there's some mystery to shooting a shotgun that only the "Secret Fraternal Order of the Gauge" can enlighten us on. Yes, there are some things to know, but it's not all that hard (or I'm just totally lost). From my experience as an amateur 3-gunner, I finished top 30% in the shotgun stages of the last match I shot shooting alongside other state and world champion shooters. That means I have a basic understanding of how to shoot the gun, reload the gun, choose the right load for the job, the right choke for the load/target, and do it all while moving and under time pressure.
I really like the shotgun and want to attend some training, but my time and finances are both limited and from what I hear from a lot of the "tactical" shotgun instructors, it doesn't sound like anything groundbreaking to me.