The McLaren was good till Bahrain, at Shakir both HAM and BUT was off the pace. After that, they had a nosejob, and voila Lewis can go fast and conserve the tyres at the same time, while Jenson is slow, and still his tyres are falling apart.
My guess is the nose messed up the CoG and made the car oversteery. Last night Ron Dennis said at an interview that Button haven’t forgot how to win, just something wrong with his car. Also mentioned that he was using different suspension compared to Hamilton. I think they both get the same treatment at McL, but the new nose works for Hamilton, while it causes Button to struggle.
If I was in charge I would risk an FP or weekend and try to put back the old nose on Jensons car, and see how he is doing with it, if he is all right, then give both cars the same upgrades. I know the upgrades wouldn’t work the same on both cars, but I would rather have constant 8-9-10th places with a car, with constant no scores.
My other solution would be giving him more ballast, just to set the balance right, I know it would be a handicap, but same here I would rather have constant 8-9-10th places with a car, with constant no scores.