Two things:
1. Comparing server capacity between two MMOs without official numbers is probably fruitless. We don't know what hardware they run on, and we don't know what they do. We have no idea how much money they each cost.
Of course, if they ever both said those specifications, then we'd be able to do something, but I don't believe that is the case here.
2. Subnumbers aren't a thing. We know nothing about subnumbers apart from very (mostly optimistic) estimates by people. What they announce was registered, once-paying or still-paying, accounts.
That is, as far as I know. Please correct me if we know otherwise.
Personally, I'd be suprised if FFXIV had more than ~300k subscribers at this time, roughly extrapolated from Alex NM clear numbers at the Eorzea Census 2015:
I'd wager that there are about ~200k. That's just me guessing though, so I won't make up my mind about these topics and their profit with that.
