There is no way to "solve" turbo lag. The compressor needs torque before it can produce boost. At the high end you can do a twin turbo. Not in an a4. And you could say something similar about having necessary power on the highway to avoid a collision.
Tldr: It's all subjective.
How so? I would perceive no difference between a turbo'd engine and a Naturally Aspirated one while driving on the highway at a constant speed. Engine responsiveness as per the parent poster would be the same within the city vs. on the highway.
There is no way to "solve" turbo lag.
I'd suggest researching variable vein turbos. BMW has done it very successfully in their e92 335s. Even resulting in a flat torque curve at very low RPM. It's impressive engineering.
I'm not familiar with what BMW did for a 335, but I do know that the 335 is quite a bit more expensive than an A4.
Variable vein enables turbos to match engine speeds more quickly. Greatly reducing turbo lag.
And I call bs. You're being argumentative. The debate wasn't highway vs "city speeds" it was highway vs cold stop.
A more advanced turbo solves the problem in a car that is $15k+ more, and I believe you that it can reduce turbo lag. For that price range a twin turbo can as well. But there is still physics that cannot be overcome.