This is an interesting one that would make for a great deep dive for sure.
From where I see it FFXIV's budget is strange.
In terms of the core in house team within CBU3, it's been fairly consistent and Yoshida has gone on record many a time proclaiming that he prefers to keep a smaller tight knit team which is fair enough. That coupled with the difficulty of actually hiring in the JP market is why I think that SE need to consider outsourcing ideas from a Mythic equivalent.
Server and system costs have definitely increased, we've had extra data centres and capacity has generally been sufficiently scaled up in line with expansion projections which is great but issues or improvements beyond that have generally been ignored or brushed under the rug (EU Duty rubber banding in Sigmascape anyone?).
The thing that catches my eye in terms of spending is the quality and quantity of voice acted sequences though. ARR had some truely abysmal voice acting that might as well have been done on Fiverr. I'm still amazed that old Cid's lines in Praetorium were kept around for as long as they were. That was some truly dire delivery and no amount of 'interference' could mask it. Compare that dross to the quality of what's followed and it's night and day. Tons of stuff has voice acting now, the quality is top notch and the actors have been fairly consistent over the years. That sort of quality can't come cheap. I wonder if that's where Yoshida decided to spend the money feeling that his team had the rest well in hand.