I think it is not a question of statistics.
First, Senna had to confront a lot of exceptional drivers : Prost (4 titles), Mansell (1 title), Piquet (3 titles) and so on ....
Second, engines were very less reliable and they had to watch their consumption because they could be out of fuel.
Third, Senna's pole position's record is not yet felt.
Forth, Schumacher raced more than Senna ( 161 GP for Senna, more than 200 for Schumacher )
So, numbers are not the only thing to look at.
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