Very popular. In some places. I'm not convinced Belgium is one of them, they have virtually no track record. At least Lindemann has sold out a Lotto Arena. FiR sold out 013 in Holland, but that is a small venue when you are talking about headlining festivals.
And of course, they're not even bothering to show for their 013 show, that'll do wonders for their popularity.
I find it quite annoying that bands don't have to put in the work anymore, don't have to pay their dues before they can climb to become headliners. It's an insult to hard working bands like Sabaton, Powerwolf, PWD and all those others who earned their well deserved place in the spotlights.