Oblivion was made by a team of around 70 people. It was not even kind of what would be considered a AAA title unless you’re just using AAA as some stupid buzzword to mean every game released by a major publisher that was sold for the average retail price...which is kind of how some people seem to use it. It’s stupid to call Oblivion a AAA title when it’s coming out alongside games like Grand Theft Auto 4 and Call of Duty 4: Modern Warfare. Nobody would say a movie that cost $100 million and a movie that cost $10 million fall into the same budgetary umbrella. You wouldn’t even say a $40 million or $50 million thing fell under the same budgetary umbrella as something that cost $10 million. Bethesda was not making big budget games until maybe Starfield. Fallout 4 had a team of around 100 people, Assassion’s Creed games at the same time had teams around 1,000 people. These two things do not occupy the same space.
That's irrelevant, it makes no difference to me, as the consumer, whether you spend €5 million or €50 million if the end product
looks like it offers that €50 million experience, a comparable scope and level of finish. As consumers, we're only interested in the development budget because it typically indicates the scope of the product on offer, but it's the latter that interests us, not the former in and of itself.
Kingdom Come: Deliverance was made for something like €15-20 million, by that definition is should be a "AA" title, and yet I see absolutely nothing in terms of what it offers that makes it a "budget" title compared to, I dunno, Skyrim or Deus Ex: Human Revolution. If Warhorse managed to achieve a similar grade of experience for a fraction of the budget, all the better for them. Similarly, despite Larian's multiple studios around the world, you can be damned certain they spent a lot less making Baldur's Gate 3 than BioWare do on whatever they crap out of late, but that didn't translate to a compromise in the experience (well, the interfaces are atrocious, but that's not a budgeting issue) and indeed it's sold as a "full price" AAA game.
In reality, "AAA" is first and foremost a price segment classification which serves marketing purposes, same way that film has the term "blockbuster", they both indicate the highest tier of entertainment in their respective mediums (and movies have their own exceptions, see District 9's $30 million budget). In normal circumstances, this should correlate to production budgets and competing products in the genre, the scope of the investment scales with what you can ask at the till, though sometimes you have exceptional circumstances, either for the better (Kingdom Come: Deliverance punching above its weight) or for the worse (No Man's Sky's devs lying through their fucking teeth). Bethesda had a somewhat similar thing going, their specialised tools and expertise allowing them to keep a relatively lower headcount while their titles, at least since Oblivion, were absolutely "blockbusters" - hell, Fallout 4, for example
"broke Grand Theft Auto V's record for having the most concurrent online players in a Steam game not developed by Valve."
A flagship Bethesda release is most certainly an "event" in videogaming and even Starfield's reception proves that - when was the last time people spent three months raging over an Assassin's Creed being shit?