This isn't true. For sure, neutering before spraying commences is the best way to go, but I've had older rescue cats that have been sprayers, neutered and they generally stopped very quickly. These cats are (in my experience) often better placed in single cat homes though.

You touch on one aspect of cat breeding I am often a LOT less than happy with. How studs are kept . I know plenty of breeders whose queens and kittens are well kept, but they fall down for me on their stud quarters and their studs existance (I deliberately use the word "existance" as I don't find it much of a life). Assuming that everything else (like heating and lighting and access to outside) are all taken care of, stud quarters are often way too small with zero stimulation for the cats and I think what irks me most is how so many breeders just don’t socialize enough with these stud cats. They’re often left in their small boring stud quarters (let’s be honest, even the best ones are just glorified cages) and never played with or petted or hugged or have a lap to sit on just human company and the comforts of the home. I find that so so sad.

The people I know who use stud nappies/stud knickers it’s more just as a safeguard for when the stud comes in to the living room for the evening to curl up with the owners while they watch the telly. I have never heard of (thank god!) anyone who actually keeps their cats in these all the time. Unlike a (human) baby nappy.... I don't think they're meant to catch pee and poop... just to stop a stud spraying against furnishings when they are out of their stud quarters.

Amethyst is right. While neutering won’t cure every spraying cat, it does cure a lot/most of them.