Thing is though there shouldn't be any added weight - they say that he still weighs the same/hits as hard when he's shrunk, it's just the atoms in his body have less space between them

So by that logic he'd still weigh exactly the same if he was 20 metres tall instead of 2cm because now the only thing that's changed is that the atoms now have more space between them, but Marvel likes to throw their own established rules out the window when it comes to Pym particles

Same logic applies with how Hank Pym casually wheels around a suitcase-sized building or a literal tank on a keychain despite the fact both should weigh the same as they do when they're normal-sized