Went into this prepared to get some laughs over people getting ass-blasted over a name's pronunciation, 'cause like Max I had no fucking idea where this "Ket Shi" pronunciation was coming from, only to actually understand it once the full context was presented.
Here's my take on this though. Obviously FFVII Cait Sith isn't meant to be an actual representation of the Scottish mythological figure (it's not like Cu in Fate where that's actually meant to be him) hell it's just a robot that is being controlled by another character for spying purposes.
That would be my position with regards to them being able to pronounce it however they want, EXCEPT that Square has always gone out of their way to give him a Scottish accent in the English dubs, showing they acknowledge where they got the name from. Not to mention they do usually try to pronounce names with Mythological origin correctly, like how IFRIT is pronounced EFREET.
So why not pronounce it correctly now and get this out there, especially since the Japanese version apparently has always done so?
Also as someone whose parents grew up during the Troubles, FUCK ANYONE from Ireland or Northern Ireland who threatens anyone with a car bombing in general but especially AS A JOKE, you fuckers should know better.