lol it is a lie as mentioned above
the games are signed, so if any data was missing or wrong, they just wouldnt play (hence why we cannot edit or patch anything)
they added data to the header in the non checked padding area just to make it look different
meaning all the games dumped with it are not clean rips
It's not a lie. They dump some datas that aren't in the same rom. Those datas are what is commonly called a "header" by most people who use 3DS roms and it's required to play online (on the gateway, you need the header and the extension renamed to .3dz).
"Dairantou Smash Bros" (Japanese dump) have the "header" so it should have been nuked if you nuke such things (but you can't really nuke it if those datas are really on the cart, that would mean it's one of the few proper dumps and that you should nuke all the other ones...).
I tried to dump my retail european "Smash Bros" cart. When you remove the "header" (gateway rom patcher), the dump is then the same as the official scene release (same md5).
So yeah, you can use the gateway to make proper dumps (same as scene ones), just remember to remove the "header" with the gateway rom patcher (you shouldn't share your personal header anyway, if it's a game that have online functions).
Without this "header", you can't use the online functions with the gateway. And if you use a "header", the save is then tied to it so be sure to keep your rom/header.
About people requesting dumps, and why some games aren't dumped, we can't know (except eshop games that are more difficult to dump, as those games are tied to your 3DS), but you can always buy the game then dump it/share it on the internet if you want it so badly, as the gateway produce the same dumps as the scene (I dumped all my games, like 30, to get the headers and all the ones I compared have the same MD5 once the header is removed).
As I was personally waiting for "Haikyu" and it finally got released, but I was ready to buy it/dump it myself if it wouldn't have been released in the following 15days after the game release (I'm also waiting for the next gateway update to access the eshop again, and if they sale the preorder bonus, Haikyu Quest, I'm ready to buy it, as no one released it yet).