Possible problem #2: Elusive Brew useage
I actually can't see anything wrong with it. It looks like he's letting it stack to 15 before he taunts, uses it immediately as he taunts and burns it at about 6-7 stacks if he has the boss. Although there looks to be a mis-taunt early on and it kind of falls off?
Possible problem #3: Dampen Harm useage
Dampen Harm has a really, really low cooldown. It can be up almost every other tank swap. If the healers are complaining about him being squishy, he's either taking huge chunks of damage randomly or he's dipping into dangerous levels frequently. Going below 50%, Dampen your Harm sir.
Later on in the fight (likely final phases) he does the same thing with Dampen Harm as he does with Guard - he burns it immediately after taunting. We don't have a lot of oh !@#$ buttons but Dampen Harm is one of them. It's possible he spiked dangerously during the 3 seconds following that taunt, but that's not my first inclination.
He does fine with it on Elegon, though.
[19:46:04.327] Lenalee casts Provoke on Feng the Accursed
[19:46:04.730] Feng the Accursed afflicted by Provoke from Lenalee
[19:46:06.592] Lenalee gains Dampen Harm from Lenalee
[19:46:06.592] Lenalee casts Dampen Harm
[19:46:07.734] Lenalee's Provoke fades from Feng the Accursed
[19:46:08.740] Lenalee's Dampen Harm fades from Lenalee
Possible Problem #4: Gift of the Ox useage
Several minutes go by without it being touched or with it just being pinged for 1-2 orbs maybe. He needs to utilize it in oh %^-* moments better. Let it pile, strafe quickly if you need an emergency heal. Me, if I've got 2 piles and it's been a while since I last strafed, I'll do a quick hop to give my healers some breathing room if I'm about 50-60% or so, especially if I just danger-Guarded. Again, it's possible he didn't need it, but with healers complaining that's not my first inclination.
Hope this helps.