I am positively convinced, that Mindfactory isn't Germany's largest retailer.
I'm not sure, they are even anywhere near the largest IT retailer in Germany.
They are certainly the one retailer in Germany, who knows how to make themselves look big, e.g. by being generally noisy and publishing their sales statistics.
Do not assume that anything they say about themselves is true just because they are saying it.
That would be like saying that tom's Hardware is the leading news publisher.
They used to lead on prices, but they paid for that via substandard service for several years.
I know because I occasionally suffered the consequences.
They seems to have adjusted both towards a median, while their logistics still suck a bit or just suffer from being in the wrong place logistically.
It kind of funny that their Danish competitors (Proshop) very often beat them on price and time-to-delivery, even though they are 400km further North.
And when it comes to service and speed of delivery, nothing beats Alternate, at least in Germany.
Just my own personal 2 cents...