Schumacher used to do crazy amounts of laps around Ferrari's Fiorano Test track too when F1 testing was unregulated.
I mean nobody is doubting how good Schumacher was but for a decent spell there he had everything going for him, best car, unlimited testing, custom tyres, soft teammate, FIA support.
Alesi, Berger, Prost, Mansell, Masa, Barrichello, Alonso, Kimi, Alboretto etc have all driven for Ferrari, with its many alleged advantages. You can add up all their victories for Ferrari, and they will fall short of Schumi.
What you claim there about Schumacher, can also be said about drivers like Senna and Prost. And unlike those two, only Schumi made a move from a winning combination to a losing one. He could have very easily engineered a move to Williams in 1996 and be even more dominant than during 1994 and 1995, but chose instead to move to the extremely problematic Ferrari.
I can also refer you to his early career, with the mighty Benetton. He routinely left his team-mates around a minute behind (Patrese, Verstappen, Piquet senior, Herbert, Irvine) He has competing against Senna, Prost, Mansell who all had better cars than he did. Schumacher was the last driver to win with a manual gearbox, and had to race without TC from late 1991 to late 1993. The Ferrari between 1996 and the end of 1998 was quite atrocious in terms of pace and reliability, yet Schumacher achieved 14 victories between those years and came very close to winning the title in both 1997 and 1998.
I can provide all the evidence of how fast he was throughout the nineties (the peak of his career, even if it yielded much less success than his late Ferrari years) but just as a slight token of his raw pace and genius witness these moments from Brazilian GP against Senna in the Williams-Renault. Ayrton Senna and everyone in F1 were in shocked disbelief to find out that Schumi was blowing the great Ayrton away with the relatively modest Benetton. Senna's shock was such, that he became convinced that the Benetton was still somehow using TC, and asked of Frank Williams to launch an official appeal, something which the Williams team rejected. Senna was a lap ahead of the 2nd Benetton of Verstapen, yet he was being thoroughly outpaced by a young Michael Schumacher:
Another thing that any Schumi naysayer may wish to consider, is that Schumacher, just like the great Senna himself excelled exactly in the same conditions and race tracks: Spa, Monaco, Hungaroring, wet conditions. Schumacher was unlucky that during the nineties, the street circuits were largely taken off the F1 calendar. Senna not only had Monaco, but Dallas, Pheonix, Detroit.
