In the past when going from tier to tier, it's been common to go for stamina in a big way at the start. The reasons are those of game design. Blizzard encounter designers balance the content around a certain expected level of gear. They work out how hard a boss should hit based on the number of hitpoints you would expect to have in that gear (or more importantly, how big the spike damage like breath or special strikes should be). Early bosses in an instance will be tuned to be challenging but possible in 'entry level gear' (i.e. gear from the previous tier), but bosses later in the instance might assume some gear from the new tier. This becomes even more true when starting heroic modes, where gear from the new tier is certainly assumed. Progression raiders could 'get ahead of the curve' a bit by pushing their stamina to the max possible (and thus reaching hitpoint entry levels for later content before they got their drops).
What I don't know is where the entry level for normal modes is. If bosses are tuned to be entirely doable in T11 normal mode gear, then they will be comfortably managed in T11 heroic gear. Chances are that if you were in T11 normal gear fully socketed/trinketed for avoidance, you might struggle?
The other thing I don't know is whether Blizzard have done what they said at Blizzcon in giving bosses something akin to expertise - i.e. making our dodge/parry (and mastery?) less effective point for point. Wonder if we'll hear about that in the Tank Q&A