Jose explained in the pre-season he didn't have options at CB so he improvised and used a 3 man CB to provide support to Fosu-Mensah and Tuanzebe, who were both starting.
Even when we play 433, the shape I see us forming most game is a 352 - with Pereira dropping deep and the two starting CB's drifting a little wide. Young/Darmian & Shaw as wing backs. Mata plays more centrally & Sanchez/Martial & Rashford/Lukaku were the two up top.
We'll have the same width issues in a 352 as we have now - (1) Because of FB's aren't very good (2) Our conservative style of play doesn't allow them to attack like you'd want. I don't believe that simply changing formations is going to magically make us better. It is our approach to the game that needs a fundamental change for us to improve.
The issue last game was that Pereira didn't suss out the danger as you'd expect from a defensive/holding midfielder. His positioning was suspect and allowed the opposition space in the middle. I think having Matic back will immediately improve us there. Pereira is a young kid who needs experience before he can play that role with authority. At this moment a #8 role with attacking freedom and where he can showcase his passing ability would be better for him.