I don't think that FFXIV would start on Parallels...
I highly doubt that it even runs on a 2010 MBP w/ 256 MB vRAM.
Actually despite a low benchmark score of 1,142 on low resolution the game itself runs decently well on the 2010 MBP. It's simply not AS pretty and has some minor slowdown issues mostly tied to loading.
As far as running under Parallels, it should run fine as the game is designed to require only DirectX9c. Performance is another story, but it should run decently well.
One thing people seem to forget is that back when FFXI came out 8 years ago it's performance requirements were virtually off the charts high. A high end $500+ video card and brand new system would net you in the range of ~3,600 on High Res (FFXI looks horrid at low res and I consider it to be unplayable much like the PS2 version. That's just my personal stance.) When it came out state of the art was a ~3ghz P4 and nVidia 5950 series card. It wasn't till a number of years after the game was released were systems eventually able to catch up to the game.
With that in mind the current 2010 MBP will run the current FFXI benchmark in High Res at a whopping 7693, while my 3.6ghz quad core w/ nVidia 8800GTS runs it at a blistering 10,168. That exact same quad-core system running the FFXIV benchmark barely eeks out 2,273!
The problem isn't with the cpu, but the graphics cards. In short, FFXIV is a graphics beast unlike anything seen before. FFXI was skewed differently. FFXI benefited drastically from processor bumps and to a lesser degree by video card changes. It seems FFXIV is the inverse (you still need a good recent CPU mind you). In short if you want FFXIV to run very well you're likely going to have to get a cheep PC and a really nice video card... or buy/use a PS3.
FFXI on the PS2 IMHO was unplayable because the low resolution simply lacked too much detail. You could be walking and not know what was in front of you till after it attacked you. FFXIV on the PS3 shouldn't have any such issues. Then again, you must also remember that the "Low Resolution" setting on FFXIV is 720P! This is by no means a low resolution, simply a lower resolution than the full 1080P.
In summation, FFXIV on a 2010 MBP is perfectly playable, but not quite a totally fluid experience that many would like/expect. It's ALL about the graphics card here.