I agree with you that there was severe incompetence on display in Pennsylvania. And although I have not watched the press conference, it sounds like a pathetic excuse for not having someone on the roof. People often say stupid things when they are making excuses.
All that said, there is always a desire to craft grand conspiracy theories about how these things happen with the implication that the "deep state" is trying to take out Trump. The fact that the dead shooter is a 20 year old nobody who was known to be a pathetic marksman really puts a hole in that conspiracy. There are probably millions of people that hate Trump that could have killed him instead of nicking his ear. If the secret service was really in on it, they could have held off another 3-4 seconds to allow the shooter more time to get more shots off.
There are questions to be answered and there is always a chance that there is something more sinister going on, but gross incompetence is far more likely than any conspiracy. And for the record....automatically saying "DEI" whenever a woman is involved is a very sexist way to go through life. Some people may say that it makes you kind of a bad person.
FWIW, there are a lot of people that say that if there is a conspiracy theory that should be taken seriously, it's that this was a false flag operation by Trump supporters to make a hero out of Trump. If that's the case...they're probably mad that the kid got as close as he did.