That's kind of the problem though, it shows the dominance of the car when he got his championships. You could say the same with MSC and Hamilton, except they both won championships in another car. And were very competitive even with lesser cars. Vettel, less so.
Hamilton has literally just 1 championship with not a dominating car and that was a season I will give you that he was decent. Not that he dominated, he was just 1 point ahead of Massa who had 1 more retired as well as some issues, to be fair everyone had more retired and issued cars compared to Hamilton that season even if we can't say he was the fastest car, if his teammate didn't get 3 retired races and some issues, I am pretty sure Kova would be closer as well.
Schumi was a great, I am not arguing against that, but Hamilton certainly is closer to Vettel in my mind. If we are saying vettel only won thanks to dominating car, then we can say Hamilton has only 1 championship with mclaren and all others are worthless, is that okay to say? I would say Schumi is great, Hamilton is great, and Vettel is great, we do not have to bring someone down to say other one is great.
I also think that we do not need to belittle the achievements of other drivers just to elevate our personal driver above them. If you are looking through twitter and through the comments on Youtube then there are always fights and arguments going on between the fans of Schumacher, Hamilton and Senna. For a lot of people Senna is still the greatest of all time even though he won the championship "only" 3 times. I also think that you can not say that Hamilton is the best of all time just because he had the most championships, i mean in the end the car is still the most important factor in the formula 1 and to determine which driver is really the best they all had to drive in the same car.