Senna's car development ability?

After glancing over Senna's career I was wondering how good Senna was at taking a car and developing it into something more competetive, like Schumacher did with Ferrari? Was the McLaren as good as it was because of Senna's input or was Prost the "brains" behind the development?

A driver's effect on the "development" of a car (always in connection with the engineers and designers!) almost certainly tails off completely within a year or even less after leaving, so McLaren's continuing strength over the years can be placed equally on the broad shoulders of Messrs. Lauda, Prost and Senna. It was always the complete package that made McLaren in those years, and that included the three drivers from the top of the pile, sometimes two at a time. You simply can't beat that!

I read somewhere that McLaren's post race or test technical debriefings could last for hours because neither driver wanted to be the first to leave, and miss anything the other had to say.

Steve