I don't think it's even that easy.
Take professional baseball players, for example. On the one hand, a mediocre veteran player can get $5 mil/yr, and I suppose that's what he's "worth", even if he tanks and/or isn't really that good.
On the other hand, the 3rd year phenom might be a far better player making a huge impact, far more than his teammate mentioned above, yet he gets paid the major league minimum ($500K+/-, whatever it is this year), because he hasn't even reached arbitration yet, let alone free agent status. There would most likely be teams willing to pay more if he were available, but his current team only pays what they have to (and maybe a tad more, but usually not much more). His "worth" would be more in an open market, but he's paid less due to artificial restrictions.
This is an outlier, granted, but an example that it's not always so simple.