Hold on a sec, I'm not gonna make any points against the rest of what you said as I'm not nearly experienced enough to say what is and isn't most efficient for tanking at a high level of play, but having just fairly freshly come out of leveling through the low level dungeons where I didn't have the gear to chain pull multiple groups, I can say you're not actually correct here, at least not when you're just pulling small groups.
Shield Bash stuns for 6 seconds, and Low Blow stuns for 5 seconds. If you have 3 enemies on you (which is all I could handle tanking when I was in the low levels with gear bought from a vendor), you use two GCDs to stun 3 enemies. Two of them are stunned for 6 seconds, one is stunned for 5 seconds. The Low Blow'ed one will be stunned for basically two GCDs, while the two Shield Based enemies will be stunned for about 2 and a half GCDs. During this time they are doing no damage to you or anyone else.
For your own damage, the two that were Shield Bashed have taken a total of 220 potency, as opposed to the 480 they would have taken if you used Total Eclipse twice, meaning you've lost 260 potency between them. The third didn't take any damage, so that's 240 potency lost, for a total of 500 lost potency.
However, you have just pressed the pause button on the fight, basically, allowing the DPS you're with to essentially get in two extra GCDs in each. Now, this of course depends on the DPS you have, with Dancer, Bard and Machinist being among the better options. But even with, say, a Monk, using a 110 potency AoE, that's 660 free potency during a time when the enemies are no longer doing any damage. And that's just *one* of the two DPS. If you had two MCH with you using Spread Shot, that's 2160 free potency in a period where the enemies are not doing any damage to you.
You aren't ending the fight faster, no, not at all. But you also aren't taking more damage. As a matter of fact, you are taking *less* damage, as the extra damage your DPS is throwing in during a period where the enemies are doing 0 damage will more than likely make them die a hit or two earlier.
Obviously this has absolutely NO bearing on later on when you're geared up enough to mass pull multiple groups, and indeed I find myself using Shield Bash much, much less than I used to now that I'm able to do that in most dungeons myself. But when you're just starting out and you can only handle one group at a time, Shield Bash is actually very useful, it saved my lowbie ass many times. Once you can handle multiple groups at once, then yes, using your AoEs is much more efficient than trying to chain stun everything. That's all I'm saying, though, in the low levels it's an absolute godsend.