If there was an attack it most likely would be outside a park like outside of the turnstyles of a park, hotel, or near transportion like on a bus or monorail.
And this is one of the reasons that security checks are being spread out, and are being redesigned to keep from having a massive throng of people lined up outside the park, where an attack, god forbid, would be more successful.
Disney has an amazing amount of behind the scenes security going on. You are on camera just about everywhere, there are live people watching you far more than you think, and there are other features as well that people don't even know about because they are completely passive and unobtrusive.
Their "security" starts from the moment you drive on property, and continues until you leave, and is not limited solely to the parks.
The current bag and security checks find things like weapons and torches, and drugs all the time. And that's what they are there for. Can someone with a pistol concealed on their person pass the bag check, manage not to get pulled for metal detector, and still get it in? Sure. Have there likely been thousands and thousands of pistols carried through Disney over the years without incident? yup.
Moving the checkpoints to where you board each means of transportation means they can be more thorough, and check each guest, rather than playing hit or miss.
Don't even get me started on the people who don't know how to set up a bag for inspection, or simply refuse to do so, or the wide variance in "security" guards.. we had one guy who just peeked into a full backpack and waved us in, and another who must have been having a bad day and decided to have the whole thing dumped out, and everything that opened, be opened. Like.. down to a compact and a sunglasses case.
And the jackarse at the International Gateway.. we went through the whole bloody pat down routine, bag check, everything, and he asked what was in the cup I was drinking... (it was a drink from Stormalong bay).. "Sorry, you can't bring a drink into the park". Sir.. I can buy one.. right there, in world showcase". "Rules are rules.. you should have just said soda." Really? The guy just advised us to LIE to security? So we walked to the benches right there, finished the drink, threw it away, went back to him.. and he made us do the whole bag check thing again.. it was completely infuriating.