The major shortcoming of that is it doesn't show walking times for some fairly easy connections between different lines and instead implies a much longer indirect route (e.g Angel to Farringdon is a 15-20 minute direct walk which is quite reasonable compared to an >11 minute journey involving train and platform changes or the suggested 42 minutes walking a very indirect route via a station interchange)

This is definitely hard to parse. Canada Water to Canary Wharf is 144 minute walk on that map LOL. It's a couple of minutes by Underground. It is about 2 miles walk, but it's definitely not 2 hours and 24 minutes!

It's about 1h if you take the Rotherhite tunnel, but if you use lungs for breathing I wouldn't recommend that.

Otherwise you need to take the Greenwich foot tunnel, which adds a lot to the trip. It may not take 2h24min but it's about 4.4 miles, not 2.