He’s now facing charges that go beyond the scope of 1/6/21, so a pardon wouldn’t have helped unless he was Carnac the Magnificent.
Issuing blanket pardons for certain individuals for unspecified crimes is a legal theory that hasn’t been tested in court. I think it probably would have been upheld. If Trump was going to get creative with legal theories in returning electors to the states, he at least could have tried one that would have maybe protected himself on his way out the door. He was dumb and reckless.