TBN can certainly be used as an adjunct in multi-hit tankbusters. The problem, however, is that you generally can't use it in isolation, and the rest of the kit is lacking, especially in heavily physical fights.
There were two reasons why I cited A7S in particular. First, Uplander Doom isn't a single hit tankbuster masquerading as a multi-hit one, like Bahamut's Claw or Gobrush Rushgob. There is a fairly long interval between each individual hit. So while it can mitigate an individual hit and perhaps negate a single stack, you're not going to eat the rest of the five vuln stack damage unmitigated. You're forced to use at least one of your longer recast cooldowns, and you don't really have many of these to spare.
Which brings me to my second reason. Historically, DRK wasn't a popular choice for A7S prog, and this was at a time when DRK had access to Foresight and Dark Dance to smooth out some of the damage, and also at a time when it didn't offer the lowest dps out of the three tanks. If a fight like this was released today, DRK would be a liability, both in speedruns and prog.
As a tank, you're generally tuned in to encounter damage patterns. Even if you're not actively tanking, you very quickly pick up on the timings of cleaves and tankbusters on your co-tank. What makes TBN fun is the fact that it keeps you "active" even when you're not. It's not just a barrier ("The law of the land? The authority of a name? These are tools cowards use to escape harm. We have no need of shields figurative or literal.") TBN's barrier may embody regret, but the follow-up Bloodspiller embodies revenge.
The problem is, while you could very well TBN every tankbuster and cleave on yourself and your co-tank, you generally won't outside of buff windows (and there too, the true value is not in the extra Bloodspiller, but in the fact that you cannot fit an extra DA on HS). I don't think that making this a consistent dps gain would dramatically drive up the skill ceiling, any more than remembering AoE timestamps and popping Third Eye has made SAM more difficult to play. If anything, many of these big hits are telegraphed 'TANKBUSTER' with an ominous auto-attack pause, a dramatic wind-up, and/or a very specific 2 second castbar, so any one of these things quickly sets off your spideysenses to pop the button. You just need to make the shield strong enough that it doesn't break if you just throw it in on a random auto.