First, not all generations are equal and so just by being the best of one generation doesnt make you as good as the best of another generation. Messi and Ronaldo are the best forwards of their generation and they also happen to be amongst top 5 forwards of all time if not top 3. There were times when Henry was the best forward, or shevchenko or raul or del piero but their level was lower than Messi and Ronaldo's. So even though they were all the best at some point in time they are not equals. So Pogba can be the best midfielder in the world today without having to equal Zidane or iniesta or Pirlo etc.. Ronaldo is too high of a standard that most players that were ever considered the best at what they do will fail to live upto.
Second, that UTD team was dreamy. They had an incredible squad with an abundance of experience on their side. Starting this season we should become at that level. There is also the fact that Ronaldo is a mental monster and a workaholic like no other. His competitive mentality is unmatched imo. Very few "best players" will live up to his mental strength.
Third, often times when people say X is the best player they are referring to the player's ability not just form. Ofcourse Hazard style runs of poor form and Milito style runs of great form are an indicator of ability but its not the only factor. Most people rate Messi higher than Ronaldo even when Ronaldo has had a better season and I dont think there is anything wrong with that. This is because the evaluative judgment that we make about players, to which form/stats are one component, also involves a qualitative assessment of their overall potential.
I think there are many players who had better seasons than pogba and are CMs (Pjanic for ex

) so he would lose on the form aspect but its the subjective component of our judgment that makes him rated so highly because he seems truly special when you watch him.
Personally I place higher weights on the form aspect (within and across seasons) when judging a player's overall ability than on the qualitative subjective aspect because there are instances when great quality fail to materialize in performances on the pitch (Cassano, Balotelli).
Thats why I agree with you that he has not yet warranted the best CM in the world title despite that I think comparing him to a young ronaldo is unfair. From a qualitative perspective only I think its obvious that he CAN be the best CM in the world as his raw talent seems significantly higher than what anyone else has. Whether that obvious quality will manifest across a season and in big moments is still an open question. I was slightly worried about his ability to deliver early last season but then he started to perform before the world cup had me more worried. I am not saying he will pull a balotelli (it takes a special mental retard to do that), I am worried he will pull a Veron where he will perform as one of the best but not proportionately to the difference in talent he has compared with the rest.
So we agree he is not yet the best (though others might give more weight to the qualitative part of the assessment over the form/stats part). And I dont think comparing him to ronaldo is fair as its too high of a standard. Comparing him to a young scholes, viera, Xavi, Pirlo or Zidane is more fitting (humans not aliens) as a standard of the best.