Most of the personnel growth is probably in asset creation. The more realistic you want assets to look the more man hours you need to put in. Even with modern tools it is just gonna take longer to make those assets. Like instead of making a human model by directly manipulating polygons that makes it immediately game ready they first sculpt it in ZBrush then retopo to a lower polygon count to make it game ready. And then add complex facial rigs for cut scenes, high res textures etc.

It’s why companies like Sony hire these studios in China and India where hundreds of people work just making assets.

Skyrim was made two console generations ago, so I'm afraid you can't use it as any sort of metric for how games are made today. Starfield's team was about 100 people larger.

I'm not a tax expert, but I think the taxes are applied after gross. Taxes on money coming in, not going out. So that ~$120k is what the company spends, but it's not what the employee sees.