The number of agents on-site would be determined by higher ups, not the agent in charge at the scene. The agent in charge at the scene would have to work with what he was given. We know Trump requested more security, but was turned down.
There are pics of two Secret Service agents on a roof with sniper rifles. If those two snipers were all that were available to work the rooftops, then there was no way to cover the venue out to reasonable perimeter. There probably should have been 2 or 3 times the number of agents assigned to a big venue like that.
The bureaucrats will try to blame the agent in charge at the scene, but the fault lies in D.C. where there was no concern with protecting Trump.
If there any drones used for coverage that is absolute proof that the SS was in on it and the personnel shortage will be just an excuse.