A fairly good point. Modern adtech is kind of the induced demand of internet bandwidth - that is, when new bandwidth is available, adtech will grow to fill that bandwidth. I guess this is also analogous to the fact that our computers are WAYYY faster now than 20 years ago, but user experience of application performance is roughly similar due to the tools used to build applications eating up a lot of that performance to make it easy to build them (electron, WPF, QT, browsers, etc).

If congestion stayed the same then ~1.5x (slightly less in reality, since each lane does introduce some overhead) the people were able to get to where they wanted (still a win!) or there was a bottleneck somewhere else in the system (so go address that as well!).

Interestingly by Braess's paradox adding more lanes can increase congestion, and removing lanes can speed up the traffic.

https://en.wikipedia.org/wiki/Braess%27s_paradox

No, merely that other transit systems have been abandoned in favor of your car lanes, which makes them an even worse option. We always scale usage relative to what is available, whether that is highway lanes or energy use.