Exactly, and I think few if any engines are overbuilt today. They're all designed to perform reliability within spec. Just the nature of the game.
It makes more sense to build to a price point that will give as many people as possible the chance to buy it, than overbuild it so tuners can extract more performance out of it.
Gone are the 2JZ days.
Modern engines are making way more power from the factory. A 3.0L Ecoboost makes 400 hp in an SUV. A 2L WRX motor makes as much HP as a 3.0L 2JZ. Fords 2.3L is making like 350 hp in the Mustang with
I also would not say the modern engines are not overbuilt. It depends on the brand. Ford seems to build some stout motors. 5.0's can push 1000 hp without opening the motor and the 3.0 and 3.5L Ecoboosts are able to get into the 600-700 whp range on the stock bottom end. In fact, a few people have hit 600 rwhp on 3.5L Ecoboosts with stock turbos.
They might not last long, but(despite the internet) I don't think a 2JZ can really do much more than that reliably. sure they are "overbuilt" in the sense that they can double/triple their hp but I think their are modern engines that are equally as stout.