Of course it's USABLE in-game, every Pokémon is except Pokémon meant to be shit like Feebas, and even then you can get some use out of it.
You're misinterpreting. Every Pokémon has some use. Some are obviously better than others, so compared to what the rest of your team may be like, Pachirisu may suck. But it's got decent defenses for when you catch it, has access to Thunder Wave and is fast enough to get it off, Sweet Kiss to confuse, Super Fang to cut down some walls, and Swift if that opponent happens to evasion spam. It's not good by any means, but it's definitely damn usable.