The London Mayor and more recently the Manchester Mayor have been huge successes in transport coordination. I don't think many people would a priori say "the best structure for a large city is fifty non-coordinated boroughs". You could make a clearer case for abolishing the boroughs (especially some of the more corrupt and incompetent ones) and running the city as a unitary whole.

The only reason the GLC was abolished in the first place was naked party politics.