Appending (as is my habit…)
This perspective (salts are primarily for mutation rather than extension) also allows you to understand why early salts were often pretty short.
It is not the case that the makers of those early systems thought a couple-of-bytes salt would be enough to /extend/ the password in a meaningful way, making it more immune against brute-force attacks. Instead, they correctly recognized that it would be enough mutation to serve the primary purpose of using a salt as a mutator, preventing reuse of hacked passwords between systems.
Since then, salts have grown as this allows the secondary bi-effect of making the passwords longer and harder to crack to be exploited - which is, of course, all fine and good.
The problem comes when the primary purpose is forgotten and someone correctly observes that using longer passwords would then make salts unecessary - that’s true with regards to the secondary effect of making passwords longer, but it is not true with regards to mutating passwords between systems.
/Mats