Up to me I can agree with both the sides involved in this theard, but some consideration:

As caster if someone (usually a damned bard) chase you, you won't able to kill him in the most of the cases, it could be fine, because I think PvP is not 1vs1 atleast up to now, but in most of cases I experienced that my attempt to use CC to stop the chaser can be really easily nullified by allied (sleep/bind) and also if you try to run away as BLM and the enemy focus you your heavy duration is really crappy, because if you use Leathargy he will soon gain resistance, but it is immediate, if u waste a Swiftact Blizzard 1 (to be honest I usually do it and then aetherial manipulation) you won't be able to use your Swiftcast for 1 min, and usually the chaser didn't stop stalking you, you can just prey to be healed and more of all Galvanized.
But the thing that make spellcasting really annoying up to me is the cone of the cast, even in surecast if someone go to your back your spell wil lbe interrupted, up to me, for all melee this is something really easy to do, I tried by myself when a BLM tried to kill me as SCH, I started run infront and behind him, after wasting some CC, he just run away.

Anyway leave a caster free to spawn his magic, how this PvP is designed, can't work, I tried to use a crafting gear vanity for my SMN, and people just left me do anything before focus fire me, I was the Best DPS of that FL.
Up to now it seems that anyway people tend to ignore SMN in pvp, and this help them a lot, instead BLM are really hated and focus fired, but the "dangerous" AoE of BLM has a really LONG cast time and it is really flashy, instead put 3 dot and spread them is quite fast and easy and it still do heavy damage.

At the end of all I think that something could be done to adjust "fix" it a little, like someone suggested, ignore the autoattack interruption, you will be interrupted only when hitted by melee on flank or behind (ignore this if in Perfect Balance or similar skills), make you interruptable only one time per 2,5 secs (I suggest only for casters, not all the other roles like healers), give a pvp skill that for few sec make you able to cast while running or able to ignore line of sight or even reduce the recast time of Equanimity of a bunch of sec any time that a cast is interrupted (for caster only).

A lot could be done and I don't think this will break anything, but obviously I aim for just a little adjustment, not for a total revolution on spellcasting, like giving to anyone silencing ability, this is another game and it has other rules, I know it could seem rough but "deal with it" :/