Obviously it's very difficult to draw meaningful comparisons between athletes that competed in different eras. Thus we have those that tout Fangio, Clark, Ayrton, et al.
Schumacher's statistics are of such a magnitude that there is nothing to compare them to. I doubt if any driver will ever top the 91 wins and 7 wdcs he accumulated in his "first career". I can understand that this gets stuck in the craws of those that don't like him. The numbers are there, they are undeniable, and no one has ever come anywhere near matching them.
Is not the greatest track and field star the one who runs the fastest, jumps the highest, and wins all the medals and titles? Is not the same true for any other endeavor? It's no different here either. If anyone has claim to the title of the greatest racing driver ever, it is Michael Schumacher.
Different eras, different:
- Types of machinery
- Amounts of races
- Financial climate (stability, driver loyalty)
- Technological climate (ability for one team to stay ahead)
Comparing eras with any degree of accuracy is therefore impossible since there are NO constants. This is the single defining principle of scientific investigation and therefore surely pretty central to any statistical analysis. The examples you give do have constants given their lack of complexity - i.e. running, jumping and can by all means be compared.
I'm not arguing that someone other than MS could be given this 'greatest driver' crown. I'm saying that even using it as a term is banal, trivial, utterly pointless affair the like of which should be reserved for shoddy tabloid journalism, children & the writing team for Top Gear.