The Norwich trains aren't "regional stock". They've got vestibules, first class, a buffet counter, and the same seat design as the 810.
I don't understand why people keep saying this sort of thing. How can we say any alternative bidder wouldn't have had similar issues?
IIRC Bombardier's bid was a bi-mode Aventra. No such thing has ever been built before, and even the pure electric Aventrae haven't exactly been problem-free.
Monopolist complacency; all eggs in one basket and all that.