Now come on. Don't throw me in there.
Pirlo, Tevez, Khedira, Vidal - great business back in the day. But those were/are proven worldclass players arriving on a free/for peanuts. Doesn't quite compare to signing Can (a good mid, but nothing special) when we've been searching for a quality mid for years now.
As for bigger numbers = better footballer, in Naby Keitas case it is just that. He is a complete allround beast and can become an absolute machine of a CM.