Bizarre that you can really think that. Buffon, Schmeichel, and a number of others have been WAY better than Kahn, who was just a decent keeper with a massive ego.
Don't think Schmeichel or Buffon ever had as big an impact in their club sides as Kahn had from 98 - 01 at Bayern and that team more often than not beat the other two top teams in Europe, Real and United, during those years and made it to 2 CL finals and 1 semifinal winning one title with of course Kahn being the hero in the penalty shootout. Kahn finished in the top 3 of the Ballon d'Or twice during those years. I doubt you find another team excelling in European competitions like that Bayern side did with the standout player in the team being the goalkeeper and not an attacker or midfielder. Kahn was invincible during his peak for around 4-5 years (and of course an incredible goalkeeper before and after those years as well) and that peak was as good as any other goalkeeper I remember. Personally I rate Buffon higher if we look at the past 25 years, mainly because I prefer his style of keeping over Schmeichel and Kahn. Casillas, van der Sar or whoever else you want to pick from the past 25 years never reached the same heights those three did. The idea that 'Buffon, Schmeichel and a number of others have been
WAY better than Kahn' like you wrote above is really silly in my opinion. If that was remotely true, he wouldn't have had the career we witnessed. Small margins, whatever way you look at it.
If we go further back into the 80's and 70's, it gets really difficult to compare. I'd say Zoff, Maier and Jennings stand above everyone else in those decades, but it's impossible for me to pick a favourite between them and the modern ones.
However, I think that Kahn's performances for Germany are a bit overrated. He's not really a legend for Germany in my book, even though it's not really his fault. He had to wait his turn for too long with Vogts prefering Köpke in '96 and '98 despite Kahn already being the clearly better keeper and then Klinsmann took away his last chapter for Germany by taking the captaincy away from him and picking Lehmann over him in '06, so in the end Kahn only played 3 tournaments. The less said about the German nationalteam at the Euro '00 and '04 the better and despite his outstanding performances up until the final in '02, he kinda fecked up in that last game. Unlikely that we would have won it, but still it matters.
I wrote the following a while ago when asked who I'd choose between Maier and Kahn:
No, not really. No one really cares who's better out of those two. In an alltime Bayern eleven, I usually choose Kahn, because that 70's team is usually well represented anyway and Kahn's impact on the team between 98 and 02 was arguably bigger than Maier's in the 70's. For Germany, it's always Maier. You can't argue against 2 international titles (and a 3rd consecutive final) with a stand-out performance in the worldcup final played at home in Munich.
Neuer has a long way to go to surpass both of them for the title of best German keeper of all time or best Bayern keeper of all time.