Nitpicking:
a) It seems that no one actually saw the school map to state that it really exists.
b) Doom maps are flat 2D blueprints with varying floor heights, they are quite unsuitable to “simulate” any building with multiple floors, not to mention complete lack of realism in everything else in the game (say, player has a speed of a car relative to the environment). There are some tricks in modern ports to combine detached level geometry into seemingly whole thing for niche maps, but those were not available at the time.
c) Trying to copy one's own school, house, or city block is the most stereotypical thing kids do when they find the level design tools. I remember quite a number of Counter-Strike maps that were nice at least visually, if not gameplay-wise, which were made that way. Surely, not everyone put that much work into a typical map made to play a couple of times with friends.
It seems that cases of overreaction to such funny nonsense that still happen after 30 years, despite everything, are something to scratch your head about.
The real situation is more complex. Harris did use game metaphors:
https://doomwiki.org/wiki/Columbine_High_School_massacre
Of course, those cliches are not unique to Doom, and were just borrowed from comics and fantasy. We should generalise. The real hypocrisy is that people like to enjoy media and entertainment about The Hero domination everything and everyone, and don't want to be restricted in consuming that, but, at the same time, they don't like to become mere film extras that get shot by the dozen when some idiot believes in that fantasy a bit too much, and decides to live the dream. This is not limited to shootings. If you hate people so much, but instead of getting guns and ammo get yourself hired by social network data extraction press, it's not a straight path to electric chair, but a “successful IT career”. If you read trashy action packed novels, and consider that crippled offspring of romanticism as ideal life, you can try that high-adrenaline amusement ride, as long as it happens in some distant land, and can be called “military career” by others.
So media and entertainment significantly shape everyone's life, but limiting that argument to a small number of scapegoat cases is cowardice.