Let's say I'm a competitor, and I find that Niel (randomly picked) is someone I want to hire. All else being equal, I offer him $100k (website says he's making $88k). He comes to his boss to say "I like it here, can you match it?" What does his boss do? Especially, if he's valuable to the company... What if I have a very specialized skill that doesn't fit nicely into your matrix? Let's say market pay for my skill is…
Oooh, or what if there's a dragon[1], and I need to be paid extra money so I can spend it on dragon-slaying gear? If you really deserve extra money, the conversation goes like this:
"Why do you make more than me?" "Because my job is harder."
Fun fact: you're not that special. Wage secrecy is good for skilled negotiators and bad for everyone else; being a skilled negotiator does not, however, ethically or morally entitle you to make more than other people. It just allows you to get away with it, and it's trivially unfair.