Grammer police got me!
MLBPA isn't the reason for offers being in a narrow range, experience and information, and as last year showed, greater use of analytics (i.e. probability that a player performs at certain levels as he ages).
Given that everyone has the same information, there's general consensus about player value, some teams might be more optimistic, some may recognize synergies, others may be cap or cash flow constrained.
But you're not going to have many "fly by the seat of our pants" GMs/Owners making stupid offers.
And players aren't going to choose location over 50% salary boost, but 10-20%, very possible.
So yeah, if Harper's value is $300M, and the Phillies offer $400M, they'll probably win, but then they lose.