Twin turbos are used for less lag. you have 2 smaller turbos spinning up faster because the Impeller wheels are smaller diameter and lighter. Of course you could have 2 big turbos then have a lot of lag. The turbocharger designs now are better than 10 years ago so the "lag" you hear about is less. You can design a turbo system to be lagless. There are varible vane turbos that offer NO LAG.

LAG can also be lessened by running higher compressions.

I have experimented with using both supercharging and turbocharging on the same engine. The results were: As soon as you get the throttle over 2000 RPM "ALL HELL BROKE LOOSE!"
There was no such thing as lag on that car.

Some guys think that lag is when you cruise the car in 4th gear at 1000 rpm and try to floor the car and it doesn't pull to 3000 rpm.
that is not lag. You are out of the power band of the engine!

Hope you understand a bit more?