Del piero would have excelled in any club. Totti would have probably done the same. The only conclusion you can plausibly draw, is that Del piero helped Juve a lot more than Totti helped Roma.
Placing Totti always above the club really was detrimental to Roma being a top club. In his best and worst of times, he was always more important than the team. So, if anything, Totti is a huge reason why Roma was never able to exceed mediocrity. In contrast, Del piero's humble attitude and patience allowed Juve to develop into a better team over the years.