The referent is clear from context. It is the plural "athletes like [Michael] Phelps", although as @Lambie commented, it could also include the "handful...".
However, a stricter--some might argue "pedantic" but this is ELL after all--interpretation of the sentence in question could lead one to take "such talent" as the referent, and because that is singular, it creates a problem given that "their" wants a plural. That may be part of what is raising a flag for you. (And it would for me too!) The meaning the author is trying to convey is not so much:
The rarity of such talent increases their market value and justifies higher compensation.
The rarity of such talent increases the market value of those who possess it and justifies higher compensation.
Whether it is worth asking for a rewrite is more a matter of style than hard grammatical fact. On the one hand the ambiguity, even though resolved by context, creates an unintended cognitive dissonance so there is a case for fixing it. On the other hand, context does make the meaning clear, so it could be left as-is. And as you can see from my example above, it may be that a rewrite is clumsy (my intent in the above was not to suggest new wording!) which might make the whole thing worse than before.
Overall, if it were me, I'd prefer it fixed, although I'd probably just copy-edit it myself, if appropriate, rather than pass it back to the author for a rewrite. That said, I'd probably be too busy to fret about such tiny details, and so I might just let it go.