Sure, Locatelli now operates deeper, but he's also played as a mezzala. So it's not like we're comparing Pogba to Sissoko here.
He's mainly deep lying and certainly more defensively minded than Pogba. Pogba has much more freedom to play particularly next to Kante or Fred. There is a lot of defensive play Locatelli does that Pogba would never do.
But even taking positioning out of the equation we are talking about completely different levels of players. Locatelli has 2 years left on his contract and seems available for around 35m spread on favourable terms with hopefully low wages. Pogba has a year left on his contract and would cost almost double that, with huge wages. They are priced that way for a reason.
Locatelli is a good player and should make a difference to our midfield. But anyone thinking he is going to come in and transform the team singlehandedly or pick up a high amount of goals/assists is mistaken. I think he'll be a solid signing and want us to get him but our midfield needs more.