I agree, he showed more potential when he was younger and if he had another Sharingan eye plus Uchiha blood to be able to master it then he would be much stronger than MS Kakashi and since he would have his own Sharingans he could have his own set of MS jutsus.
He would be above Itachi, Kakashi showed more promise than Itachi as they grew up. Kakashi graduated from the Academy at 5, became Chunin at 6. Itachi graduated from the academy at 7 and became Chunin at 10. Kakashi also learned lightning, earth, and water elements which allows him to copy jutsu from those three elements and as an Uchiha he would have 2 Sharingans, will not suffer from using a lot of chakra as he did in canon, and will have powerful chakra as all Uchihas have (Indra got the Sage's eyes and powerful chakra).
Also Kakashi lives up to 33 where as Itachi died at 21 so Kakashi would have been much stronger since he was a genius himself growing up and would only be stronger being born an Uchiha. He would have gotten MS when Obito "died" since he already blamed himself for Obito dying by saving him and Sasuke said Susanoo can be used by those wielding 2 MS so he more than likely would have at least a Susanoo but the 2 MS for each eye varies for each user.