Have a horrible feeling that we're getting to the nub of the problem. If we wish to have a collaborative carrier prog, it's likely that the French would want us to get aboard the Rafale prog to offset some of their development costs and also to counter the NATO-wide Dave buying frenzy.
However, logistics and sanity are likely to suggest that setting up parallel support lines for two essentially similar (in terms of technology, generation, role) a/c in the UK ain't gonna happen. The step-change that Dave may offer (not to mention the workshare) gets around that.
Bottom line (as it always has been), collaboration where sensible (eg larger purchases of common items on the ship like the GT, DG, motors and principal radars etc), but not for collaborations sake (eg workshare arguments).