It’s all a matter of the vehicle and what your goals are- sure at some point you need to modify everything else, but a turbo car gets a lot further to start with for a lot less money. I grew up tuning old Volvos and Mercedes and they were so well made and undertuned from the factory you could just about double the horsepower for next to nothing and they were still reliable. Early on they even used massively oversized turbos that had a ton of lag but could really have the boost cranked up. European cars, especially older ones tended to be heavily overengineered - with the drivetrain, cooling system, suspension, brakes, etc. massively oversized compared to Japanese and American cars.

> undertuned from the factory

This seems to be a big component of then vs now. Previously companies lacked precision modeling and simulation and so often simply overbuilt parts.

Now, costs have been cut and fuel efficiency standards are much higher, so systems are more tightly engineered from the factory.

Sure - but my point is the hobby is nowhere near as popular/mainstream as it was before