Bearing in mind that the tax on fuel is completely proportional to how much fuel you use, and is also weighted to tax turbine users (which use the airspace services to a much greater degree) modestly more, and (most importantly) the tax has not gone up in decades, it is a reasonable compromise.
The avgas tax will be a much smaller percentage of the overall cost of fuel than it has traditionally been.
Main thing is, we are not creating a new category of tax or fee, and are not creating a construct which would discourage appropriate use of air traffic control services and thus increase dangerous operations.