LA's got their mobility to get into position, HA's got the shield to get a bit closer, medics can heal pretty well I suppose (And have great options with ARs anways!) Lacking any options to get into position easier or survive the task, is it still a good idea to roll with a pump shottie on engi?
The thought "HA shield allows to get close" is ridiculous. HA shield will give you time to make another shot, but it won't help to break distance. Sure HA will live longer in direct combat, but that's the combat function of the class, and it has nothing to do with shotguns, as it would work just as well with any other weapon. Any class can charge in a building and shove a shotgun in enemy's face. Don't have to be an LA to do it. What LA will do is to fly in from behind and score a multi kill, but PA shotgun will be just as effective on engi as on any other non-LA class.
So using it as you move between cover while getting closer to targets to save your shield and HP for the actual fight is a ridiculous concept?
Running in the open like a big slow glowing target is ridiculous, yes. Unless the enemy is a newbie, he'll kill HA before he gets close enough or deduce HA is armed with a shotgun and keep distance.
If you're forced to run in the open between cover, the overshield can mean the difference between losing HP, which can be detrimental in a fight, and losing shields. So it's a lot easier to maintain your HP and shields if you can quickly react with overshield to block a few shots as someone clips you getting into cover. As opposed to constantly getting chipped away or pinned down.
While overshield gives you more "engagement time" it does not give you more engagement flexibility. A shotgun requires the ability to get close without being shot at because even with overshield you can't take enough fire to just charge in to close range. Furthermore you also would be better served to be firing immediately with your full health advantage than charging in, losing your health advantage, and then trying to land a killing blow with the shotgun. In the end, any gun you use is a useful as you make it. A shotgun engie can be as useful as anyone else if you look for opportunities to exploit its strengths. LA's are more capable of finding and creating such opportunities, that's all.
I've had some fun using the G1 shotguns with slugs and a laser. Those headshots are rewarding since they give a nice OHK within 22m. I have also had good experiences with it almost always 2 shotting HAs using NMG. Usually they run down their shield far enough that you can 2 shot them. Also great for bunny hunting, as most medkit poppers will be OHKed by the slug to the body. Just keep in mind that its a pretty high skill playstyle compared to the usual pellet shotgun shenanigans. Higher risk, higher reward.
I use shotgun because usually am defensive, and have machine gun turret when I want long range combat. Also if you are already use a enginer with a sundie or tank its a good secondary weapon for clearing out a person who is running around right next to it, if they get too close under the range of your main gun you can shotgun them. If you are hanging back and someone assults you, you can counter assult with shotgun. big disadvantage I found is that while it can istantkill enemies, you can die pretty quickly closing the gap, or just missing before you can do the shot.
Pump shotguns take a good while to get used to, but, the biggest thing you'll have going for you is surprise. No, seriously. NO ONE expects the Engineer to have the point-blank death machine that a pump-shotgun is. Heavy Assaults, it's expected, and Light Assault, it's practically a given anymore, but Engineer... no one will expect it. Sure, you have to be super creative to use it well, but, once you get that dialed in, it's absolutely hilarious.
