Modern vs Medieval, what time is it?

[Iscah]

I think that could actually explain why Exarch had such a hard time with it. On Norvrandt, he can make the Tower do stuff for him, but across dimensions it all comes down to his own control of magic. Even Y'shtola has a known tendency to flub her teleportation spells, and Raha was a Bard back in 2.0 when they only had like three buttons to worry about. It was probably way more than he could handle.

He talks about it in 5.1 specifically. It's partly because he's not naturally a mage and has to draw on the tower's energy, but also the spell itself has to be tailored to the intended target, which it why it goes wrong when he grabs someone else instead.

Y'shtola isn't flubbing her spells though. Flow is working exactly as intended, which is to say teleporting the target "anywhere but here" with a chance of ending up in the aetherial rather than physical realm. It's explained back in Heavensward (when they first worked out that she cast it) that normal teleportation spells require incantations and take some time to cast, but Flow is instantaneous - which is why she's used it as an urgent last resort.