For CP2077 vs HL it's pretty obvious why it would need to be a lot larger, with the sheer volume of art assets, story writing, level design, voice acting, game

For CP2077 vs HL it's pretty obvious why it would need to be a lot larger, with the sheer volume of art assets, story writing, level design, voice acting, game balancing and engine sophistication required. But I'll be the first to echo your sentiment that there are massive diminishing returns on team size. Of course in many ways AAAs have dug their own pit of despair with this, they throw so much investment into it that they need to make sure they appeal to as large an audience as possible and cram as much content as possible in, while also having an eye to DLC later down the line, the economics demand it. Hence why CP2077 had to desperately try to get it to work on last gen console, otherwise they'd be immediately removing a massive portion of the market. As consumers we can get as much enjoyment out of some indie level gamer. I for one have play way more hours of The Binding of Isaac than any AAA title I've played and it would have been a fraction of the development costs.