I like Herrera, but you're being conned if you think we shouldnt be after an upgrade in his position.
Of course we can get better players but there are much bigger problem positions to sort out before his is one to do. Having no holding midfielder other then Carrick being #1. Then our center back situation. Then Ibra being our only competent striker at 35. Then our wingers, who when on form, are very good, but still lacking in an actual winger. Martial is class but plays like an inside forward. Mkhitaryan is class but is a playmaker playing out there. When both Martial and Miki are on form the balance is really good actually, but having nobody to bring off the bench and play like a proper winger is a huge thing we lack.
Having nobody better then 6/10 at left back is another big problem. Compare our left back performances to the ones of Valencia and you can see how much we lack. So yeah. CDM, CB, LB, ST, winger are all positions that need to be looked at throughout our squad before Herrera becomes someone that should be changed.