It makes me wonder what would happen if G.fast had never been done how fast FTTP deployment would have been with a lot more engineers working on it.
Wouldn't have made much difference to be honest. It wasn't an either-or at that time regrettably, there was robust opposition to the investment required to deliver FTTP. Openreach told government they'd deliver way more premises passed than were feasible with FTTP and set about the work on that basis.
At some point the priority changed, within government, to quality as well as quantity and gigabit-capable rather than just 'ultrafast' became a thing.