Any payment the government forces you to make is a tax, in my opinion. And I see no difference in the “government” forcing you to pay a TV license versus bundling it in tax revenue. As you wrote, the same government can just preclude that amount of tax revenue from being altered by the “executive branch”, if that is the goal.

But otherwise, the “government” can always alter the tv license fee, or the tax. It’s always under their control, and changing its label doesn’t do anything.