Have you missed the last 10 years of US politics? Because the fact of the matter that the rich, by virtue of their wealth, are able to legally absolve themselves of their nominal tax burden, is common knowledge. This is common knowledge to the point that it was a major subject of the most watched US presidential debates in US history. While players selflessly give their time and money to charity, they also both have the right, and ability to use that to reduce their tax burden. They also, by virtue of their wealth and social standing have the ability to retain some of the best tax attorneys that also work to legally reduce their effective tax rate. As such, this makes their tax burden at minimum a non-factor towards their decision making process in UFA. There is nothing in here that points to me accusing anyone of anything other than working within the law, as it stands today.
And as an side to FlashyG, I would look up 'Jock Tax' which is nominally how pro athletes state taxes are calculated. But, Stamkos still, nominally, paying state taxes for at least a third of the games he plays.