The other thing about SE combo is that it's a 33% increase on healing returned via Inner Beast and Bloodbath. That is very significant, and for that reason alone it should be kept up.
Fracture doesn't have the same benefit. It doesn't increase your survivability. It doesn't increase your enmity. And the damage gained is minimal. Yes, it's only 1 GCD every 30 seconds, but it's also only a gain of about 70-90 potency every 30 seconds.
To put this in perspective, Let's say you're doing the alternating rotation (BB -> SE -> BB -> SE) which is imo best for using Fracture and probably best in terms of DPS.
You've got 4 full combos in 30 seconds. One Butcher's Block combo is 630 potency. One Maim combo is 610. So in those 30 seconds you're putting out 2480 potency worth of attacks. The "Average" potency of one of the global cooldowns is ~206.
Adding fracture in swaps one of those "average" globals for a 300 potency global every 30 seconds. It's a gain, but it's only a gain of 94 potency. When you're talking about 2480 potency over the time period, adding an additional 94 doesn't make a huge difference. We're talking something like a 3.7% increase in DPS.
Yes, it's an increase in DPS. But it's not an amazing increase.
It also ignores the fact that it's a "costly" ability to monitor, mentally. You have to track the duration on the mob, you have to ensure you're top on threat by a good margin. You have to (or should) be sure you have 5 wrath stacks. And you have to only use it in between full combos. For this reason, it should probably only be used in "comfortable" situations, such as when you aren't taking heavy damage, or you aren't having to fight for threat. (though my biggest threat competitors seem to be white mages).
I don't know if this is right. I'm pretty sure Storm's Eye will wear off before the 2nd butchers block hits, if you go SE -> BB -> BB -> SE -> BB -> BB as your rotation. But I could be wrong on the timing of the SE debuff going up.