Additionally, yeah, it's true, competitors might not be able to realize the same value in the same space. Competitive advantages exist. Spreads between value and salaries will exist, and some companies might have bigger spreads than others because they're more able to realize value. I agree with all of this.
All I am attempting to do is refute the claim that there's no relationship between value of work and renumeration for that work ("[t]he value someone creates has nothing to do with their salary"). I don't dispute that we can create toy examples where that doesn't happen, but they aren't effective refutations of the general point.
(Economists say demand and supply are elastic, I think.)
matthewowen's argument is not assuming the labor theory of value is true. It's just pointing out that, other things being equal, if the demand for X increases then the demand for X-makers' labor increases too; hence X-makers' wages increase.
For example, a person doing the exact same job at Facebook is going to provide more value than a person doing the exact same job at Twitter which is going to provide more value than a person doing the exact same job at a brand new startup. The Facebook employee might be producing $1m and the Twitter employee might be producing $200k. In that instance Twitter can't pay more than $200k and Facebook has no incentive to offer more than $200k.
Or maybe a more concrete example, if I am the head of design for Ford, the value I produce for Ford is always going to be more than I can provide by myself because I have no way to put my skill set to use in a new company. I don't have access to the supply chains Ford does. I don't have access to the factories that Ford does. I don't have access to the labor market that Ford does. If I wanted to actually compete with them, it would require billions in funding behind me like Tesla.