The problem is that SMS would probably cost 70-80 mill pounds. So he won't be a backup to Pogba.
And if you have seen SMS play, he too kind of walks around like Pogba, he isn't the most mobile but has better positioning defensively.Not to mention he plays for Lazio in a much more advanced role, even as a #10 at times.
If we intend to play with a DLP,we would need midfielders who can keep the ball and press the opposition.
If we intend to play a Pogba - SMS - Jorginho midfield, both Pogba and SMS will be walking around, mostly near the opposition box as neither are very good at pressing or defensively.That would expose Jorginho or whoever is playing as DLP and our midfield would get over run quite easily. And where would that leave Matic, who has been very good this year.
That is why a Carrick replacement doesn't make much sense.If we buy a DLP, are we going to play Matic - DLP double pivot with Pogba as #10? How good is Pogba as #10? Not very from what I've seen, even Mou said he's a B2B.
The best thing to do IMHO is to go all out and buy the best available #8 who can control games,who can press and pass well, who can tackle and assist thus relieving Pogba of the pressure of being the sole creator and also lessening his defensive duties. And for a backup DM, either buy a young prospect or mold McTominay into a Matic like CDM.
I agree we have no competition for Pogba but IMO SMS is not the answer to our midfield problems