You can (under)rate our players as much as you want, but we will beat Roma because this is what we do best. Winning is in our dna. And I think our midfield even without Marchisio and Khedira is reasonably strong one. You are terribly underestimating Pereyra by calling him mediocre, which he clearly isn't. Sturaro coped rather well against Real's midfielders few months ago and has been showing incredible progress with each passing game. Pogba, Pereyra and Sturaro are combined better than what Roma can offer atm.
I am not saying we will lose to Roma, I am saying they have a better midfield in terms of players. Whether our mentality will make us ultimately win is a different question. I can say Dzeko is a better striker than Zaza without having to believe that Dzeko's team will win.
Player for player, would you like a direct swap where we give them Pereyra and Staruro and they give us Pjanic and Radja?

Any sane person would take this and run and be awarded the title of greatest transfer guru of all time.
I don't think I am under-rating Pereyra when I say he is mediocre. He wouldn't start in any top team. He is a good player to have for rotation. His best position is AM. We will be playing him as a CM under a 3-5-2. That just adds insult to injury.
Staruro is still a big question mark. We have seen very little of him and he is still very young. If he is the next Gattuso then great. If he is the next nocerino then thats not very bad. We still don't know. A good match against Madrid doesn't make him at any level close to Roma's guys. Santon had great games against Ronaldo too and look how that turned out. Its still to early to tell.
So on Paper, Roma is definitely better in midfield. In reality we dont know whose midfield will dominate but its more likely theirs will(given that they are better on paper). We have never seen the trio of Pogba, Pereyra and Staruro as CMs in a 3-5-2 before.
In short,I dunno where you get this confidence in our midfield's superiority when 1) you've never seen these 3 players start together before in this formation, and 2) you know that Roma's midfield is better on paper and has been working together for years.
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What i say is that roma has players better then both sturaro and pereyra, but combined with pogba, we are better because those hold their own
Technicaly, when talking about a 352 against roma's mid 4, we should consider the wingbacks aswel.
How do you know that? They've never played together in these roles before while you have seen Roma's group together for 2 years now.
It wasn't a walk in the park when we had Pirlo, marchisio and Vidal man. Where do you get the confidence to say that we easily have a better midfield?
Get realistic. Its nice that you have so much faith in our players but don't let that blind your reasoning.