Everything ive seen save for posts from 2012 indicate 50 per 3 (since 60 per 3 would mean it would take a very very long time to go out of tp given the average combo is 63 tp (70/60/60), gcds are 2.5 and people have latency/in and out of combat etc). Either way, the point stands you are only generating 13 tp per use of shield swipe compared to your average combo. A flash eats of a full gcd, and gives you a full gcd worth of regen of tp. That tp is more efficiently used in a combo instead of swipe. If TP management is an issue, using swipe is less optimal than flash, and you will do more damage per TP with goring blade or the royal combo (average damage per tp).
It feels nifty to slap a button cause it lights up, but swipe is kind of a trap. If you have tp issues, use flash. If you dont have tp issues, use other abilities.
Second part is the crux of the issue. If you are in a bleeding edge progression guild, the only way you are holding threat off war ot's and good dps is staying in shield the entire fight and spamming rage --> rage--> goring. Other tanks can drop out of tank stances (my war co tank most of ravannah ex in deliverence)--that is because all of their damage applications effect their emnity increases.
We have the issue of:
1) Sword Oath doesnt have its damage effect by increased emnity
2) Flash deals no potency to be magnified
3) Our threat combo does the least damage out of any aggro combo, which coupled with naturally low ways to magnify our damage (darks do this largely by OGDS, about 2000 potency a minute oGCD vs our 1100, or via straight modifiers in the case of wars (maim/zerk/lulul all dat damage).