First of all, I'm no fan of the Borismaster and I've said before. It's a vanity project and solves a problem that no one knew existed. However, look at the sums involved...
The additional capital cost of the Borismaster is approx £60k per vehicle (so 600 vehicles over a 15 year life) this equates to about £2.2m a year. However, this is partially offset by them being bought by TfL so leasing costs are removed. The total figure for additional staff was estimated at £37m per year but that's for all 600. As we now know, many will instead operate as OPO anyway so that figure will be much reduced. Whichever way you slice it, it's a long way away from the £100m to bring parity to driver wages. So does the money come from an increase on fares?
Why is this acceptable? Well, it depends. Firstly, the cost of living (especially accommodation) varies across the capital. Secondly, these are headline figures on rates of pay.... what else is paid to represent take home pay? Surely if a driver is getting paid £3 per hour less then surely there would be an issue with retention? Why do you think Arriva can pay £9.30 and get staff if they can work elsewhere and get £3 an hour more?
My late father was both a TGWU shop steward and a bus driver. He worked at a depot where drivers got paid a lower rate than others in the same company. He'd have loved to have been paid more but he was realistic enough to know that, had that happened, the depot (which was predominantly rural operation with a reasonable amount of tendered work) would've been rendered uneconomic and would've closed.
Lastly, to compare with Deutsche Bahn is to fail to understand the complexities of German employment legislation. I work for a German business too, yet in the UK, we pay different rates of pay at different sites for essentially the same work.
To my mind, the scourge of retailers (and others) employing people of zero hours contracts is a more pressing priority.