Fun fact: Fire Emblem Heroes is the ONLY mobile / gacha game I have ever played, and I just quit a few months ago. It was very good. Yes, it was gacha predation. But the art was excellent and certain game modes (for much of its life) were very good. The only other mobile game I have come close to playing was Genshin Impact, and I try not to play any of that stuff. Nintendo understands that you need great mainline FE games in order for Heroes to even exist on mobile; it's not going to detract from core game development. Heroes (fan service) only works because of the fan devotion for the main games.
In fact, I'd say the state of things is very good since we get Fire Embelm on the big screen with docked Switch now. The last entry was not good, but the future is bright.
FE: Heroes has generated 1 billion dollars in revenue. Off of basically neglible development resources, other than the art. That is insane, yes. Think how that happened starting back in 2017 and we haven't seen anything like it since. I don't think Nintendo is going to be able to replicate that kind of success again.
I also think you are going to see more great remakes and premium edition FE games on Swtich because of its pull. That FE1 Anniversary box was VERY cool. I believe they can still be had for relatively cheap on the Aftermarket, like
~$150ish. That was one of the nicest fan-service projects Nintendo has ever put out, this gen.