The short answer is no ... but he could be.
Of course, that partly depends upon your definition of best. In terms of sheer brilliance, it would be difficult for Sovereignty to surpass Arrogate. He’s not that type of racehorse, but his 3-year-old season has a very good chance to be better overall if he can defeat older males at least once. Some, myself included, might consider his season to be better right now.