My response to your three points is mostly “free will”. The hockey player and team owner enter into a contract of employment. Both agree to the terms, and both should abide by those terms. Up until the contract is signed, both sides can walk out the deal. The hockey player can try to find another team to play for; the team owner can look for another player.
So this makes the fact that hockey players have a short working career a bit of a moot point. All professional athletes should know this and make good decisions accordingly. Many professional athletes have the opportunity (even with current tax rates) to salt enough money away to never have to work again — if they decide to keep a low consumption lifestyle. But if they want big parties and sports cars, well their small fortune will be blown away. Should we blame the tax man for that?
Some professional athletes become venture capitalists. Good for them! But they should be subject to the same laws as other venture capitalists. Their short career should not be an excuse to justify a lower tax rate.
Again, the hockey player should into his profession knowing that he is going to be taxed at the 50% rate. If he does not like that, he can go find another occupation.