It's like you don't realize we have far more exciting youth coming through our ranks and on loan than Roma have.
Even if all of them miraculously become world class, that'll take much more than a couple of years while our backbone is retiring or getting too old.
This is us in 3 years without purchases (selling Pogba and Vidal):
New GK
New RWB - Ogbonna - Bonnuci - Old Chiellini - New LWB
Pereyra - Asamoah - Marchiso
New Striker - Morata
Here you need atleast two world class CMs to play with one of marchiso or asamoah just to maintain our midfield level and we'd have pereyra and one of asa/march on the bench. You need a world class RB to replace Licht and an above average lb and 2 bench players. Your strikers department has only Morata and so you need atleast one top striker and 2 above average subs. In defense we'll only have an old cacares as a sub so we need 2 more defenders one of which atleast has to be above average. We'd also a need a new top goalie.
This is Roma in 3 years without purchases (selling strootman & Pjanic):
New GK
New RB - Mbiwa/Catsan - Astori/Manolas - New LB
old De Rossi - Naingolan - Florenzi
Iturbe/Ljajic - Destro - Gervinho
They need a goalie and 4 fullbacks two of which has to be very solid. Their midfield only needs adequate bench players or perhaps one top level creative starter. In Attack they are set and only need 1 bench player at the most.
We have much more buying to do and our core players will all be lost while they will only need to patch things up. On the other hand, we should have more money available since we are more wealthy and because we should be able to make more money out of selling vidal and pogba than they will out of pjanic and strootman.
They are better situated for the future as their core & squad are generally much younger than ours. If we are to maintain our advantage then we have to do a better job at replacing our core players than they will and at a tighter budget since we'd be spending on more players (quantity) then they are. Marotta has to out-perform sabattini while allegri has to keep the ship moving.
I am not saying that they will be better forever, we will always be financially superior to them and so we should come up on top as soon as our transition phase is over. All I am saying that if both teams do their homework right they should do better than us in the very near future before we make a come back. If we manage to stay on top through the transition then Marotta has to be credited for that (unless roma collapses on their own).