I think Nier Automata is a fantastic game, one of the best ones I have played in a while, same with Witcher 3. Yet my value in money is "only" 50-80 euros (expansions and shit from Witcher). If you consider this its not odd at all that they are transitioning to a freemium (mobile) model. The amount of resources (not just money but also developers and time) it takes to create an AAA+ game is considerable and the potential revenue seems to much less then for a freemium/mobile game.
But if this continues who will want to invest a lot of resources into games like Nier who are a one off 50-60$ purchase?
These games are fantastic but to me but there are only a few of me compared to the millions of people who play Fortnite or other freemium games. The only reason seems to me is that you try to co-exist with these freemium games rather then compete with them (as you are offering something else). Yet you are very unlikely to make the same amount of revenue as these games I feel. Hell I wouldn't be suprised if the Final Fantasy mobile game (which is crap imo) already is making much more money then the latest Final Fantasy games. Turning existing IP's into mobile games have already proven to be insanely succesfull (FGO, Pokemon GO, etc). Hell I see ads for the Assasins Creed Mobile game.
From a business point of view Diablo Immortal is not weird at all and I wouldn't be suprised if it becomes very profitable too.