Complete or well rounded is not the same as saying he is the best. Iniesta has been the best for some time without having a defensive side to the game. He was just exceptional in possession. Pirlo was the best again because of his unmatched vision and long passes without any semblance of a defensive side to his game.
As things stand there are players that are better than Pogba at particular tasks. Iniesta is still much better in possession. Modric is a much better passer. Kroos and Pjanic are better passers. Vidal is better than anyone else defensively and can hold his own very well offensively as well.
Pogba and Vidal are the best well-rounded CMs in the game in terms of skills set but both need to bring it to the pitch much more consistently than they did last season to be counted as the best midfielders. Vidal was the best B2B at one point and seems to be returning to that insane form again. If he can keep it up next season he will become the best again. Pogba needs a season where he brings it in the CL and doesnt have a long rough patch like he did in the first part of the season.
It depends on the role you are talking about...
Iniesta is indeed something brilliant attacking wise while his defensive duties are not remotely close to Pogba therefore if you are looking for an attacking midfielder Iniesta is better
If you are looking for a central mid thats another thing...
Vidal is definitely someone who you can Pogba with but Pogba has surpassed Vidal this year (last year Vidal had the slight advantage but Pogba has improved)
Modric is a better passer of course he is so does Pirlo but it doesnt make them better...
As for the last part - It is called adjusting to a new role...
By the way It seems it will be a cash only deal as Real seem to take Morata back as confirmed on FI
So Batshuayi here we come
Meanwhile we are linked with getting 3 players instead of Pogba - Valencia's Andre Gomes, Palmeira's Gabriel Jesus and Sevilla's Grzegorz Krychowiak
Gomes is good and has great potential but currently he is overrated! Jesus is probably another overrated Brazilian while Krychowiak will give some defensive stability!
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P.S it would be so funny to win the CL next season without Pogba just 1 year after he leaves for Real (not to mention Vidal`s reaction after leaving for better chances of winning the CL...)