One of No1e's problems at USO is that he has never defending his title. Defending titles is a very important factor for me. To make Ultron the GOAT of USO, he has to get 6 titles. 5 titles for GOAT USO can not be enough, due to Federer's series of 5 titles in row in a years 2004-08, which are four successful defences. To overcome Federer on USO, Djoker needs 3 titles.
At the moment, Djoker is not in the group 5 greaterst players at USO history. More titles than Ultron have Federer, Connors, Sampras, McEnroe. The last place in the Top 5 belongs to Lendl, who has three USO titles, as Djoker, but also two successful defences, even managed to complete the hat-trick, this record has already reached only Big Mac and Fed at USO. If Djoker gains the 4th USO title, will overcomes Lendl, but he will be behind Big Mac (because Big Mac also owns the hat-trick). If Ultron gains the 5th USO title, will overcomes Big Mac.
If Djoker had 5 USO titles and had two successful defenses on his account, he would have exceeded Connors and Sampras, who managed only once to defend the title.
In this thread, they are opinions, that Djoker's advantage is 8 participations in the finals, but 5 of them Djoker lost and the lost finals are double-sided weapon. They show the very good consistency of the tennis player, but also his weaker success in the finals.