Anyway, the analysis shouldn't necessarily be between the current Mercedes and other cars, but about what might happen over the next three seasons. With Ferrari catching up, Williams still there or there abouts and the prospect of Mclaren-Honda getting it right next season, it's unlikely that Merc will continue to be quite as dominant as they have been. Therefore, they would quite rightly want to keep hold of one of the very best drivers on the grid.
On that basis I think the deal is pretty good for both sides.