In the end, it seems like the senate had very little power (as Germanicus stated) they were a puppet of, it seems everyone. The senate's power would have to be restored, first off.
Secondly, one major problem with the armies is that they were in competition with each other. Two generals might be able to work together if they had to, but most of the time, they were out for their own personal glory. Allowing generals to have the triumph meant that every one wanted one and it caused armies, loyal to their respective generals, to do all sorts of things they shouldn't and wouldn't usually do. Armies it seems were no longer loyal to the Senate, or even to Rome. They were loyal to their general.