That's just self delusion horseshit. Any guy who sits down and rationally thinks about it "hum, so Jane slept with 20 guys before me, what are the odds I am the best lay of them all? A few of them being completely primal matings fueled with drugs, alcohol and a week long party atmosphere and our own sex now having a bit of a mundane flavor since we literally had sex a few thousands times by now."
A woman, unless she directly seeks it, will avoid confrontation and will tell you any white lies she thinks will make you feel better about yourself. So yeah, no shit, unless you married a cunt, she's not going to say you don't make her top ten. Instead she's going to say you're the best sex, your cock has the perfect size and you're a world class kisser. Again, duh.
Unless you marry a virgin or a girl with very little sexual experience, you're a god damn moron if you think you're the best sex you wife ever had. You just have to sit down, run the numbers and compare the potential circumstances to realize you aren't likely to top her list.
This goes both way, if you lived a little yourself, your wife shouldn't come close to top your list either. Freaky girls who keep sucking to get you hard after you came 5 times and who let you put it anywhere you want aren't for dating, or for marrying, they are for fucking and memories of said fucking.