Europe doesn’t hail autonomous driving as revolutionary because it is a super dense area with a well established train network.

Density doesn't have anything to do with it the US is as if not more dense if you subtract all the void in between places. Even taking the void into account the US has twice the population density of Finland (16.4 vs. 33.6 per km^2^) yet Finland manages to have public transport in its urban areas. Places like the east cost are significantly more dense than practically anywhere in Europe. California has practically the same density as Spain.

And it's not like the US don't have an established rail network, either -- they just let it rot and operate it in a way that doesn't make rail a viable alternative to driving or flying. With the same rail policy as Europe there'd be a HSR sleeper train from New York to LA, HSR which also in Europe would have to be constructed, first, all that track from the age of industrialisation doesn't do high speeds.

how much money would you be willing to bet otherwise?

How much riots, money, and deaths is the US wiling to bet on autonomous driving to avoid raising intersections when the street gets its periodic make-over, anyway? It's upkeep in general that costs money, rebuilding them in a sane way while you're at it costs little more to actually less: Most of their streets are way too wide.