>someone must have done a cabbie vs satnav challenge

I'd argue it's been happening on a fairly large scale for the last few years. That Uber is competitive is a good sign that the Knowledge isn't nearly as much of an advantage as the cabbies would have you believe, but nor has it been completely eclipsed by tech

I wouldn't be surprised if Google accounts for the London Marathon. Does it account for the opening night of a new show in the West End? I highly doubt it.

I don't think Google maintain their own data for rail travel, and the data sources aren't that good, so I doubt they'll be accounting for engineering works unless either they are scheduled far in advance or they've been happening for a while.

In my experience it takes time equivalent to a bunch of people having a crap journey and Google collecting that data for Google's instructions to change, they're not pre-emptive based on expert knowledge, they're reactive based on collected data.

They have. Just search on YouTube. The ones I could quickly find were about 10 years old unfortunately and not exactly extensive experiments.