But for Rare plenty of time has passed. What do they have to show for it? Sea of Thieves and a Killer Instinct game for the whole of the last decade.
Killer Instinct was a Rare property but not developed by Rare. And you're underselling how hugely successful Sea of Thieves has been. (Not that I understand it; the game seems incredibly shallow, but it found a huge audience.) We have a pretty thorough accounting of what Rare's been doing, and Sea of Thieves happened under new management at Xbox that wasn't running the show post-Nuts-and-Bolts.
It wasn't all that many, and most of it likely came at expense of what would previously be multiplatform games. Zenimax would still be releasing games if they hadn't been acquired. Sure, exclusives benefit them but this "competition" was really a net loss for players who don't have Microsoft platforms. It came at expense of the third-party market.
The same is true of Sony's acquisitions.
If you want to talk about scale, the industry in general, especially the type of game that sells these consoles, is so much bigger than it was in the 90s. If you're buying a studio in an attempt to compete with a console outselling yours 5:1, you're not buying a studio with a few dozen people who sold a few hundred thousand copies of a game. You're buying a company with hundreds or thousands of people who sell millions of copies and a large percent of those customers buy DLC and microtransactions, because that's what moves the needle. A large portion of those customers, by the way, only bought a PlayStation for that game, because that game was associated with PlayStation in the marketing, even though it was also available on Xbox.