It should also be noted that while they are invasive, they have been established (in my part of Canada) since at least the early 1700s. I wouldn’t go importing mullein and planting them on purpose, but I will also not destroy them on my own land. They are like a mini-ecosystem all of their own. And when the bees are done with the clover they can be found on these mullein more than any other plant in our ‘yard’.
And while technically invasive, they are neither aggressive nor hard to manage ( if you are not trying to manage a million square KM of national Park ;) )