T13 adds

[Sleigh]

Flash has something like 2300 damage worth of aggro attached to it in full STR gear + DW axe (correct me if I'm wrong but that's what a quick test by eye showed). It's not unreasonable for BLM to do that with a crit Firestarter, or a DRG's Full Thrust crit + AA, or a BRD with Barrage + Hawk Eye + Bloodletter within a GCD, etc. I'm not seeing why you'd willingly want to roll the dice against those things with a Flash pickup when a Skull Sunder has more damage, sustained aggro, advances wrath, and will hold from everything a non-tank can do short of a C3 (and I once had a lucky crit Unchained Skull Sunder beat an ill timed C3 in this exact scenario).

I have as average a connection as they come and the only way a wyvern gets past a stored 2 is if I let them. That includes DPS mashing tab target + their fastest attack, because I'm doing it right back.