The Mk-XIV was an unmitigated disaster on those lines, but was the only plane the Brits had that could hope to compete late war, so they flew it anyway.
Unmitigated disaster? What rubbish. I think you are making way more of this than need be, Shooter. Regardless of any handling issues Spitfires might have suffered, the average RAF pilot certainly did not think the XIV nor the IX was as bad as you make out. Here is an example: 130 Squadron Spitfire XIV pilot Ian Ponsford;
"The Spitfire XIV was the most marvellous aeroplane at that time and I consider it to have been the best operational fighter of them all as it could out-climb virtually anything. The earlier Merlin-Spitifre may have had a slight edge when it came to turning performance but the Mark XIV was certainly better in this respect than the opposition we were faced with. The only thing it couldn't do was keep up with the Fw 190D in a dive. It could be a bit tricky on take off if one opened the throttle too quickly as you just couldn't hold it straight because the torque was so great from the enormous power developed from the Griffon engine."
Do you think an average service pilot would state that the XIV was "the most marvellous aeroplane at the time" if it was an "unmitigated disaster" as you claim?
Jeffrey Quill claimed that the XIV was; "...something quite outstanding – another quantum jump almost on a par with the jump from the Mk.V to the Mk.IX." If the aircraft was as much of a dog as you make out, then Quill wouldn't have claimed it was outstanding. After all, he flew every mark of Spit there was.
I also don't understand why you think the development of these aircraft was protracted. Nine months elapsed betwen the first flight of the first Mk.VIII, JF316 with a Sixty Series Griffon and the first production 'XIV, RB140. That's not that long to incorporate a research programme and to put a new type into production and service.
Shooter, you need to let go of this, because there is plenty of evdence on these pages alone that your hypothesis is incorrect. Before you mention Spitfire the History, I have a copy right here on my book shelf and I have studied it at length for years. I have spoken to Spitfire pilots, both WW2 veterans and warbird pilots of Spitfire Vs, IXs and XIVs. None have said anything that matches your description of how these aircraft handled. Everyone I have spoken to about flying the Spitfire has said that it is one of the best handling of any aircraft of its era.
Here is a quote from Tom Middleton, a warbird pilot who has flown Spit XVIs and XIVs; he states that "The XIV will always be my favourite aircraft of all time. I adored everything about it." "The Mark XVI is easy to fly [bearing in mind a XVI is a IX with a Packard built Merlin]. It instinctively tells you when it is out of balance." as for the XIV, he calls it; "...a seductive gypsy woman, a wild and sexy thing." "It was heavier on the control, but much more powerful and a good deal faster... ...whilst not difficult, it was quite demanding to fly."