Not really. I'm sort of surprised anyone would see wrestling today like that. People trade victories back and forth all the time.
Now, realistically I'd never expect Ziggler to stand a chance against Lesnar. But winning one match on one night doesn't automatically say that Ziggler is better than Undertaker. It says that for some reason on that night Ziggler pulled something off. I don't think it would reflect badly on others that Lesnar has beaten.
I agree. Not that this type of logic isn't without it's validity, but I find it annoying more often than not when people use it since you could probably nitpick match results like this all day if you looked hard enough into it. I mean, you could say that Bray Wyatt is better than the Undertaker since he beat the guy (Bryan) who beat the guy (HHH) who beat the guy (Brock) who beat the Streak, especially with all these matches no more than a year apart, but people don't really see it that way.
Not that Ziggler would be my pick to defeat Lesnar or anything (although that match would be awesome), but even if he did, they could simply say that on that night, Ziggler showcased more heart, more courage, more spirit and more determination than he ever had before, and the result was the best performance of his career, one that will probably never be duplicated. You could also book the finish like Taker pinning Kane at WM14, where Lesnar gets his shoulder up at the end, but just a second too late.