Caster stun is also useful for tanks.
Tank grp with a single caster likes their target to be stunned to stop it kiting and bearing in mind their damage output is less than a caster set up (and they do not have the range) they need to stop the kiting.
Reducing interupts is also going to have a big impact on casters - unless you can balance this by making tanks less susceptible to magic damage then you may as well wave goodbye to tanks because then they will hit for less, have no range and willnot be able to interupt - so what is left for them ?
)
)