Yes, it is 100% security theater. Without x-rays, anybody who was so inclined could easily bring anything they want (including a disassembled rifle and ammunition) into the parks. I won't post the methods one could use but the imagination doesn't have to be too creative to come up with ideas.
They are finding things that people don't try to hide. On the occasion that they find a gun it's because the person either forgot it was in their bag or didn't know there was a bag check so they weren't actually trying to get by security with it. Same with the CBD oil.
The TSA has enough trouble finding things with x-rays. Disney security CMs aren't going to have great success poking around for a few seconds.
With the exception of MK, someone could just whip a rifle out of a bag as they reach the bag check and run into the park and start shooting. The security CMs aren't going to stop them. Maybe one of the police officers would put them down before they kill too many people but the officer still needs to draw their weapon in a surprise situation so there will be some delay in response.