There more to Xeno's explanation than just "I hate it, and I know I am the minority". He created a video about tanks shortly after he leveled every single one to 80.
He does acknowlegde that the shield itself is great, even better than every other mitigation action in comparison (inv excluded ofc). It's effectively 20% mitigation, but it keeps your HP save, while all the other CDs do not. The shield is not his issue.
His issue is that it is not just tied to your damage, but also to one of your highest damage action you have. It not pop'in is a huge damage loss, and it is a trend only tied to DRK for some reason. In HW DRK actually gained damage by using CDs, namely Dark Dance for Low Blow and Reprisal procs. In SB, TBN was equivalent to 140 pot while granting a only 20%/10% shield, even pop'in it was neutral at best, only in Grit it was a gain thx to Bloodspillers Grit potency. In ShB however, TBN is equal to 500! pot, and it grants a stronger shield than before.
Xeno also said that TBN has a huge potential to be really good action -maybe even the best- as long as it's not tied to your damage the way it is now!

imho, it was already bad designed in SB, but less flawed than it was today. It's the same with Inner Release being a bad (or lame) design, but it was less flawed in SB because it did the most damage and generated the highest enmity -in addition to Unchained- on pull.

Here comes the more controversial part
Let's make a really stupid comparison to SAM' Third Eye. Current Third Eye procs on 1 single damage, doesn't cost anything and is a slight dps gain if proc is used on Seigan for 15 Kenki.
Now imagine Third Eye gets the "TBN treatment": instead of mitigation, you gain a shield, it would cost 25 Kenki, and let's you use 1 "free" Shinten when proc'ed -but you gain nothing if it doesn't. You do the same damage you'd do otherwise, and if not, at least your healers don't have to heal as much. Ain't it great design, right? /s
Every SAM would start a revolt against this.
But worst case it's just 1 lost ability, just use it at the right time! The problem is you, not the ability! /s

Again, SAM is a dps, and DRK a tank, that's why it's a stupid comparison.
Still doesn't change the fact that tying mitigation to your damage -in a negative sense, as in "loss, no gain"- is a bad idea -yes, it even feels bad using it, once you start to think about the fact, you'd have used a Shadow ability anyway.
Neither does it change the fact that using TBN as soon as it comes off CD is bad mitigation. It's just a bad rotation in terms of dps. But dps is what matters the most. It also doesn't guarantee you that it would save a GCD heal.
So, are you good tank because you mitigated most damage, or are you a good tank because you dealt high dps? Where is the line here, what helps the most? Did you save a GCD heal and was it worth? Or did you (over-)mitigate so hard that oGCD heals have gone to waste?

I am sorry that this post isn't as composed as I originally wanted it to be. Guess, I am a little frustrated that the tank role -that I play for more than 3 years- has taken such a beat. The whole role is flooded with flaws, scarcities, and cuts, in addition to the dev team reacting very slow and reserved to any changes whatsoever -on top of the current situation we're facing which delays the excruciatingly slow changes (if any) even further.
Warrior can mitigate/heal more with Nascent Flash if they deal more damage, Vengeance can give additional damage. Gunbreaker can enhance HoS with Brutal Shell (even tho its just a 150 pot shield), and Paladin Intervention with Rampart or Sentinel. Dark Knight is just there, and tells himself "well, at least I come out dps neutral."
And literally every single person I know -those who also played the current iteration of DRK- said that TBN is "just so bad". They confirmed the shield is strong and nice, but the proc mechanic is just so annoying, they end up using it like 3 times in 15 min -outside of Ultimate. In Ultimate, they just play DRK (or healers want them to play it) because TBN just procs on every auto-attack, so there is no risk, which makes it "just so good". Again: without the risk, TBN is "just so good". Otherwise it's "just so bad".