Previous reply is well past over-stuffed, but wanted to address this part here as well. Because, I really like this part, and I want to see more AoE / ST crossover.
That's... pretty damn cool. Yeah.
At present a 2.33 Dragoon can spend 4 GCDs in rotation across multiple enemies to mass-CT and fire 5 or 6 Gierskoguls per minute, total of ~9340 to ~9940 potency per minute total, iirc. That would be about 387 potency per GCD, more than a Ring of Thorns x3, less than a RoTx4, less than a DSx3. So it's already a dps loss, but you'd have near infinite TP (the rotation doesn't support you most costly spender, Phlebotomize) instead under a half minute's worth. (And it needs 30 seconds per CT to get that full duration, even though they die so conveniently timed... Ouch.)
(1000 - 69 TP/s + 20 TP/s) --> about 20 seconds' worth of TP at 2.33 GCD DS spam. So, if you really needed that TP for later, it wouldn't be a bad idea. But until then... Very, very niche.
But that's just... bleh. And this is probably the ONLY job in which single target can even make a cross-over, because of Gierskogul's AoE being generated by ST attacks (F&C/WT). Everywhere else, there's virtually nothing. Monk mixes the two, via DoT-cleave and Rockbreaker, but you can't really call that a crossover apart from the Demo vs. RB decision (full Demo deals more than a RBx3, but less than a RBx4, and is as efficient as an RBx6). DRK's is just the obvious multi-Scourge and then whatever MP allows (SE is worth more healing and damage than an DA-ADx3 and costs less, so the decision's obvious for self-heals, unless you're at the edge on AoE enmity, which probably just harkens back to AD vs. Unleash, where both give the same enmity but AD deals more damage and costs more mana...). In short, it's kinda shitty.
And honestly I don't know what would be the best path to try to fix it. I personally want to see anything that looks like a cleave be a cleave (looking at you Spinning Slash), but I've no idea if that will work either.