Well, yes, it's decided by pure power, but it's about a certain 'type' of power, or power in a specific type of circumstances, which she was more suited to and - as Pantani_lives says, is more conducive to the type of efforts mountain bikers put out, hence why you have people like Langvad on the podium back in 2019, PFP winning in 2014 and Jolanda Neff in the top 10 in 2016. You'd think a "pure" power test would mean seeing the likes of Chloe Dygert winning, and nobody really expects to see her on the podium on the Mur.
The Mur is so often about timing, van der Breggen always said she had her place that she went and she would ignore everybody else until then, because if they went earlier they wouldn't be able to sustain it when she upped the pace, and if they did and they stayed away, there would have been nothing she could have done about it.