I don't know about London, but many places systems like this results in terrible working conditions for drivers. Pay is lousy, shift arrangements are in some cases insane, like work from 5:30-10:00 and then 14:00-17:00. Minimal time in between routes to go to the toilet and so on.
Yep, it does! However the net benefit to society at large - and being public transit, to the less privileged in particular - is still gigantic compared to any of the alternatives, and this is blatantly obvious if you've been in multiple countries/locations that use this system, as well as ones that don't use it. The job is generally still better than driving for e.g. Amazon, as well as honestly a whole load of 3D jobs[1] that we rather forget exist and people carry out every day, including in "wealthy" countries.
Perfect is the enemy of good. This is the #1 thing other progressives need to learn. Everything is a tradeoff.
