I think you know that in modern football hype is expensive. Potential, too. Pogba is the best player of his age in world football, and we can only expect him to get even better. However he's not the finished product quite yet and what we are selling is a player who promises to be the best in the world but who seems to require being settled in order to develop and play well.
At the start of last year we were in disarray and Pogba failed to step up. He shrank away from the responsibility. When things got more stable he played better. Him moving to that United team will be a similar experience. Perhaps he has learned from last year and will be able to be the talisman that United are paying for, but it's not a guarantee.
I do love Paul but let's not forget that Modern football doesn't necessarily rank players just by their ability on the field. With regard to his price we have to consider the marketing, the fact that we're selling to an English club, the fact that we don't actually want to sell him, the fact that his contract isn't about to run out. All of this stacks up next to his star quality and his considerable ability on the pitch and results in a high price tag.