Fully justified. It was the only thing he could do. The Mayor of D.C. told him in no uncertain terms that he did not have the authority to call out the National Guard without a specific request from her.
General Milly, in an act that ended 233 years of constitutional presidential authority, as Commander in Chief, over the United States military, said he would refuse and the military would not be used in Washington D.C.
Trump had, more than once, offered the use of the National Guard to the Capitol Police and they, more than once, explicitly refused that help.
So now tell me what Trump was supposed to do. He'd been very plainly told that he had no authority to do anything.
Are you really going to suggest that a public call on Television for the rioters to go home was going to get people engaged in a riot, not sitting at home watching TV, to go home? How was that going to work when the rioters have no TV to see the message?