I think the obvious solution to your problem is that
you need to maintank Brutallus.
If you're looking for an alternate solution however, I'd recommend letting your Protection Warriors know the following:
- A Mainhand Glaive is only useful in low rage situations while in tanking gear. You should probably also let your Prot. Warriors know that in high rage situations they are losing 80.65%* of their threat from Heroic Strikes, while using a Mainhand Glaive.
- This will probably cap their threat somewhere around 950 TPS, on a fight like Brutallus, assuming they're actually using a decent rotation and are grouped with a Windfury Totem, which they probably are not if they can justify giving a Prot. Warrior a Mainhand Glaive over a Rogue.
*(2.8 Speed / 1.55 Avg Tanking Wep Speed) - 1 Hundred Percent = 80.645% difference in weapon swing speeds. In English: That Brutalizencrusted Longblade of yours is 80.65% faster than a Mainhand Glaive.