There is plenty of opportunities where you can cast pyroblast against good players (or braindead how you call them, derp). Not every hero has stun to stop the cast, you can cast it from behind the trees, walls or from the bushes, you can have melee heroes to block the way to you, you can use it on runners under 50% of their hp, you can use it when enemy team sits in crowd controls. Even if someone on their team holds his CDs to counter your Pyroblast, it's still good trade, it's not like Kael is useless without his ulti. And saying 'phoenix will always reposition enemy team' is just not true, because it's raidus is crap and damage is minor, so at best it will just make a squishy or two move a bit, which usually isn't a big deal. I think Pyrobalst is much better ulti overall.