I've played many seasons with > 200ms and gotten gladiator. I don't think I've ever played a season with under 100 ms constantly, gotten 9 glad titles. One season I played from hotel internet on a laptop even for my last minute push.
While latency is awesome, it shouldn't be an excuse, I know a lot of R1/Glad level players who always play with > 100 ms. The only thing that's noticeable with my play when I play on east coast vs. west coast servers is melee interrupts. I feel it's also harder to play a healer for the opposite reason, though I've gotten 3x as a healer.
If you can improve your internet, do so, if you can't, there's a LOT of other things you can improve before it becomes all that's left (hint: it will never be all that's left). There's a lot of lower ping services you can do which do work, I've used a lot of them, they help, but it really depends on why your latency is so high. Also, consider changing servers, likely a closer one would improve your latency.
Edit: Noticed you're from NZ - I've played with a lot of people from Aus/NZ, their latency never was of any issue that I could tell, it was mostly just their play times. I would try a "lower ping"-esque service, though 200ms should be playable.
I have to disagree with Merite saying theres no issue playing with 200+ MS. As melee it's a constant uphill battle. Ive been playing 2k+ as Rogue/warr and Feral and it gets very frustrating (Arena, I dont do RBG's). Also playing from east coast to west coast is hardly in the same ballpark as playing from aus/NZ.
Of course latency is never a good thing, but it's probably not as debilitating as you would think. It's possible to compete at the very top even with poor ping, though you might have to work a little harder for it than you would without that latency. I would expect the hardest thing to deal with would generally be interrupts (outgoing and incoming), but this season you also might get gibbed by swifty macro hero shaman/palas because you can't use a defensive quickly enough. The latter is just poor game balance though and hopefully isn't representative of the game's future.
If it's something you're interested in doing, I wouldn't rule it out based on high ping. There are so many factors for a new PvPer to understand and master that it should be quite a while before latency is even a top concern for you. Once you get to that point you may find yourself at a slightly lower rating than you truly deserve, but I hardly see that as a reason to avoid trying.
Edit: In response to the title, Mes famously plays from NZ on a terrible connection.