To explain why Fracture shouldn't be used, in any other situation, consider this: the best basic rotation is SE>BB, which has exactly 100% uptime for SE (e.g. no overlap in the SE debuff). Any time you use Fracture, you're cleaving off the debuff from one of the other combo finishers (Fracture breaks combos and, as such, you always have to start fresh after it). As such, you're getting a 300 potency attack but removing the 11% bonus from either a 280 or 270 potency attack, which is either an 11 potency loss (280 / .9 = 311.11) or breaking exactly even (270 / .9 = 300). You're actually losing slightly more than that because you're slowing down your next Inner Beast by 1 GCD as well, but that's harder to directly calculate.
If you're trying to maximize damage, the only attack you should use other than SE>BB (for any case that is *not* the predescribed UBIR attack string) is Inner Beast, because it's effectively a 400 potency attack (300 / .75), so, at worst, you're gaining 89 potency from the loss of SE uptime.
The problem with Fracture isn't the cost (it's actually pretty efficient given that it's 300 potency for 80 TP, which is 3.75 pot/TP; BB combo is the closest competitor at 630 for 190 TP, which is 3.315 pot/TP; it's "expensive" in that it increases your consumption per GCD, which, in any situation where you could feasibly run out of TP, ends up being a DPS loss thanks to buff/debuff uptime). The problem is the damage itself being too low coupled with the fact that it is a GCD that doesn't contribute to your Wrath to some extent.
Honestly, if the devs want to encourage WAR to use Fracture, if they don't want to just increase the damage, they should give it some chance of providing Wrath stacks on each tick (it's 10 ticks, so a 10% chance per tick would basically make it, over time, a single GCD for a single Wrath stack; this is more efficient compared to the other Wrath generator combos which are 3 GCDs for 2 stacks). That way, even if it decreases your damage by reducing debuff uptime (it might actually end up being a minute increase to damage via increase Wrath stack generation), at least it increases your mitigation by giving you faster Inner Beasts.
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(speaking to using Fracture on jumps only)
How many jumps like this happen over the course of a fight? With Levi EX, depending upon DPS, you'll see between 2 and 7. With Titan EX, you'll see about 3-4 jumps. On Garuda EX, it'll happen about 4-5 times (once for first jump, once more for each add phase). On Ifrit, it's just straight up 3 times (when he jumps into Hellfire, he's immune to damage; it's when jumping into charges that he still takes damage).
At most, you're talking about 700 extra potency, but, on average, closer to 400. For a tank, that's about 400 damage. Unless you lose the fight by less than 1k damage, your "optimal Frac usage that you should always do" isn'y going to mean anything. Hell, if you lose by that much, I can pretty much guarantee you that you probably could have done any number of other different things (use of tank CDs can actually cause there to be a variance of several thousand potency over the course of a fight) with greater impact.
It doesn't matter how much you argue that there are *some* GCDs where it's better to use it than others, if the number of GCDs where that is true is in the single digits, your argument is pointless: if the event occurs so infrequently that it dilutes the value of it to the point where it is completely and totally unnoticeable (and, honestly, is going to have less impact upon your total performance than natural variation in damage due to the RNG will), whatever you're discussing is pointless beyond semantics.
There is no practical value in using Fracture, *whatsoever*. It's DPS neutral and mitigation-loss in normal use (thanks to uptime loss and Wrath stack prevention) and, in the conditions where it's a DPS increase because uptime and Wrath stack prevention are a foregone conclusion, said increase is so small that it might as well not be there.