It'd be interesting to see actual reliability statistics on the B5s since they've moved to the X21. Without seeing the actual stats, I'd hazard a guess and say that reliability on the X21 has actually gone up. I certainly see less off-brand vehicles on it compared to when the 16 plate StreetDecks operated.

In my view, the issue with the 'reliability' is probably less down to the vehicles being less reliable, and more down to the vehicles being down for longer due to issues getting parts, which compounds resulting in multiple vehicles being off the road at once, whereas in the past there would just be one at a time, in rotation.