Zelda: Tears of the Kingdom devs explain why it was a much bigger overhaul than you'd think

That sounds like a very interesting talk. Would look up if I can find the full video.

I think it was pretty obvious that this game was lots of effort. Even if not counting the sky and underground, ultra hand itself was a game changer. Though, I guess if you don't know how these things work, you may feel it wasn't that much of work.

The pre-existing game engine with a bigger world and couple of new mechanics, in other words.

Not that TotK, or that approach to sequels, is even bad: I just wish Nintendo did less furiously masturbatory self-back-patting about how revolutionary it supposedly is. It is what it is (an acceptable if underwhelming sequel IMO), and Nintendo is what Nintendo is - a bag of dicks.