This is also true. I also remember reading about how Yoshi-P really likes how efficient his team is currently set up (the same reason he brings in guest creators to break the efficient mold they've established). I've also studied programming and have even attended a GDC event in-person myself (with a student discount of course, tickets are hella expensive even with a discount) so I can understand where you're going with this.
But at the same time, it's inevitable for them to have to hire new staff as well. Developers are human beings too, some developers may want to move on from the game while some may need more rest and a reduction in workload. When these happen then we would be left with less manpower and no replacement.
Another thing to consider as well is to spend resources in hiring third party support. I don't know if the FFXIV team outsources any programming work (which sounds like a nightmare in my opinion) but I know that they do outsource art assets from third party companies and companies from even outside of Japan. Consider the state that the Viera & Hrothgar are in; since you also studied game development (I assume so since you watched GDC seminars), then you'd know that the adding a new race is an exponential (non-linear) increase in workload since they'd have to create even more assets for every new armor they make in addition to recreating past assets to work with the new races. While they'd have to tighten their quality control if they decide to outsource more art assets, doing so is a lot less demanding than recreating assets themselves.
The addition of Viera and Hrothgar is just one of those cases where I think Yoshi-P's team bit off more than they can chew, and now there are fans chewing them out for it because these new races can't wear all helmets. This is how a team expansion and increase in resources can really benefit the game in the long run and why I think this type of investment is worth the risk.