There are plenty of American cheeses that win the top prize in international competitions. Six of the eight cheddar categories at the following competition were won by US cheeses.
https://wccc.myentries.org/contest/results?event=63&submit=S...
https://wccc.myentries.org/contest/results?event=63&submit=S...
There actually are some good US cheeses, although oddly enough not a single one of them comes from Wisconsin to the best of my knowledge. (Vermont, Iowa, and California in case you were wondering.)