I mean, it's not though. Rooney after 2010 for the most part was inconsistent as feck in his performances within 90 minutes but had his moments of quality that made him worth it (til the last few years). Pogba is inconsistent as feck, makes some amateurish passes and touches at times but then also has some passes, dribbles, touches and shots from range that turn everything on its head. Rooney was productive enough that he was worth it and made him a quality player still. Also he was a forward, and that was his main job at the end of the day. Pogba is not a forward, he's a midfielder. He doesnt score often. He creates a decent amount of chances but hes never among the top players in pure chances created (was productive with assists tbf though). Hes not productive enough as a midfielder like what Yaya toure was, or Gerrard or Lampard, to make a slack overall game worth it. So he needs to fix that.
Central midfielders like Pogba don't score too many goals, it's not part of their game overall and even Pogba has said this because he's not focused on his goal output. Stop putting him above all other central midfielders. KDB is not a central midfielder. Dele Alli is not a central midfielder.
Yaya Toure had one anomaly of a goal scoring season for City, albeit it was awesome with 20 goals. Fair play. But overall, his club output of goals and assists according to TransferMkt for first tier domestic seasons (i.e. La Liga, Premier League) is 74 goals / 49 assists in 33,626 minutes.
Pogba: 39 goals / 45 assists in 14,759 minutes. You double his minutes and his output is higher than Toure, yet his minutes is still fewer than Toure.
Lampard was a terrific player but the stark differences are there with Pogba in terms of style and expectation. Lampard also played with the likes of Makalele, Essien, Ramires, etc. who allowed Lampard to roam forward and make his trademark runs. He was a top player. Pogba is the much better passer, better vision and ability to drive/dribble through midfield. Lampard wasn't bad at these either, far from it, but not on the same level as Pogba.
And Stevie Me is another fantastic player and his blood and guts, captain style endeared him to many...but he wasn't even the best midfielder in his team...Alonso says hi! His best goal scoring season came when he played in the hole behind Torres. And he's always had that freedom to run about and put himself about because he had Alonso, Mascherano, Benayoun, Kuyt, Henderson, etc.
Overall, Pogba's output is trending much better than an traditional central midfielder like Toure who many considered world class which he was, maybe for not too long but he was. Lampard and Gerrard were never known for their two way player and more for their goals (especially Lampard) or their blood and guts captain drive (Gerrard).
Pogba has improved year over year in a United shirt, yet missed matches due to injury and suspension...and he has much more to give. Let's continue to see how he gets on in a United shirt. He's trending upward, now he just needs to play his game and be better. I think he'll be fine.