I don't think it's that massive, especially because you should be figuring out a salary range within the first 1 or 2 conversations with the company regardless. For software engineers anyway, not sure about other less-hot markets.
Yes, this law will disproportionately benefit sellers of labor with a worse supply/demand situation. Price transparency is always better for the party (buyer or seller) in the worse supply/demand situation.
Why? Prices are the signal to market participants for allocating resources. It is the whole basis of free markets and why they work.
What would society gain by obfuscated pricing? Assuming the goal is to benefit all of society, and not certain individuals who happen to be able to take advantage of arbitrage scenarios.
