Roma has been doing fine in Europe for two years in a row now and they still have hard time with Italian league for example. That should tell people how hard it is to be good at Italy week in and week out. I am not saying they are not good, but being consistent and being good are different things.
If we look at their best ever game, I am sure their talent level is better than most clubs, should have been top 2-3 team according to how great they could play on their best day. But when that's not sustainable and inconsistent, that means you end up also playing very terribly as well, much worse than what they could play. This ends up with a result where they just end up losing games and that's not alright, it really hurts them a lot.
Even though the quality and talent of Roma's players is good, I think to be a Serie A champion is still not enough to compete for title with Serie A players from other top clubs. Unless AS Roma gives Mourinho the freedom to buy 2 top players, maybe we can see Roma competing to become Serie A champions.