Suspension of belief still has to be slightly logical. Sure, I can believe in Magic and stuff like that, but really? Alien Race with technology beyond our world is really going to be destroyed by RPGs and WW2 Era munitions? Not so much.
Ignoring Torch's apparent unwillingness to discuss this topic, I will say that Suspension of Disbelief matters on a few things. One: How much are you willing to invest into the setting presented. Two: Internal consistency. It doesn't matter if it's all powered by Phlobtonium, it either has to be explained, or in the way Star Wars does it, make it seem like it's so normal that no one within said setting makes much of it. To continue Star Wars here, Blasters? Speeders? Spaceships that can and can't break the speed of light? All fantastical things, but the characters take it as normal, so the audience is encouraged to as well. And lastly, how 'grounded' in common things is the setting in question. In Star Wars, yes, Laser Swords, and Blasters and Speeders and Starships are all fantastical, but there are analogs we can identify, and as long we are willing to just accept some things just are (Like the Force) we can enjoy the film.
Of course, this is all subjective, and people have different levels of things they are willing to accept and things they aren't. As long as they explain WHY World War 2 stuff can hurt the bad guys, I'm willing to see it. Of course, it might just be so fun, you don't even notice.
Like in Independence Day, that fact that A) Earth styled computing worked on the Aliens. B) You could create a virus using Earth code. C) That an Apple product would be able to have a virus created on it. Not to mention the length of time needed to do so with any sense of reliability. But the movie was a lot of fun so no one actually questions that until AFTER the movie. And even then a lot of people just shrugged and moved on.