Why late Roman armies became smaller and more centralized

What did the last Roman legions look like?

They evolved into smaller mobile and frontier forces that were more flexible but demanded greater central coordination.

The later comitatenses and limitanei were smaller, more flexible formations than the classic legion based in one region. Several brigade-sized forces could be coordinated by a Caesar or Augustus rather than placed under a single divisional commander. That arrangement increased the burden on the centre because more separate units required direction. It was also politically attractive because no subordinate held one large regional army with which to rebel. The answer presents reform as a trade-off between operational control, flexibility, and coup prevention.