They are both valid criteria, depending on your perspective. But the perspective that matters here is the perspective of the owner of the Android OS.
The EU's ruling was that Google needed to defuse the situation where their market position of Android was furthering their search engine dominance. The EU did not demand that Google give up the economic benefits of developing a popular phone OS. So Google even though Google must offer choice of defaults, it still has the right to sell spots on the list, so long as there is choice.
So the perspective that matters in choosing spots on the list is Google's, subject to obeying the EU ruling to offer alternative choices. Google's economic interests are aligned with getting the highest price for the spot. There is no reason why DDG ought to get the spot for free.
