Hmmm. Yes and no I8apex
I think it's fair to say the Ducati has been the most difficult motorcycle to extract the best from over the past eight years. But you confuse competitiveness with rideability.
Stoner was a bit of a bolt from the blue in 2007 with the obvious advantage of being on Bridgestone's whilst Yamaha and Honda ran Michelin's. 2008 showed up the pitfalls of the flexi tubular steel chassis but Stoner still won his fair share. Stoner was happy on the GP9 CF chassis; sickness ruined that season. 2010 the first year of the hard 'n' 'stones, which seemed to suit the Ducati less than the other marques. Stoner became frustrated with Ducati's lack of progress but also said when they got the narrow set-up window right the GP10 was a good machine.
Now given Stoner was barely faster than himself in 2011 on the RCV over 2010 on the GP10 in like on like comparable conditions one would suggest the 'Pramac' machine was still a competitive motorcycle - as all previous 800cc incarnations had also been. Competitive doesn't mean easy, and yeah Stoner was the only rider to win on the thing. But so was the Terrapin at Yamaha until Lorenzo rocked up, and so was Dani at HRC.
Look at Nicky Hayden as a bit of a control. Mediocre on both 800cc machines - RCV and D16.
The D16's are difficult and it took someone of Stoner's genius to extract the final performance percentage no other rider has been able to achieve. Is that Ducati's fault? The very best magnify the shortcomings of others and the easy target is always the machine. Since Stoner left they haven't had a top shelf rider capable of pushing the thing to it's limits. No doubt they also lost direction with the Rossi concocted plan to try and turn the thing into a M1 (contrary to what he initially said about him having to adapt to it - ha, ha.) of which they're still trying to find their way out from the mire of.
Given his woes with a couple of relatively minor spec changes in 2014 I doubt Lorenzo is the man for the present bike at least. But does anybody believe Marquez couldn't win on the GP14? I say the bike is capable.
Cal's problem was (as always) his mouth. He knew the thing would be difficult but pumped himself up as as hard man willing to do the hard yards. Just as with Rossi before him he appeared to have been defeated by the motorcycle almost at his very first test of it. Contrary to his proclaimed British Bulldog spirit, he quit - very early in the piece too. And all the while second (third really given Marquez is a class of one) tier rider Dovi has run rings around him. Oh dear.