Still not the best that no one ever was. In fact, his Sinnoh championship was his best run, but in Unova, he made backwards development. Says a lot, right?

Does everyone forget that literally every person in the league has all defeated 8 gym leaders some point in their journey? Take that into account and realize that everyone in these competitions are relatively skilled.

Ash has made it into top 16th and higher in all of his league competitions. That's a completely valid placing.