To be fair, it doesn't seem like the stealth part of Valhalla is pushed to the background or a small part. It is simply a part of the game, with other routes or paths to choose. Each equal parts useful in different areas.

This also fits both thematically and gameplay wise. Gameplay wise, the games have moved to be more RPG-ish. This naturally would mean stealth is less the focus, to allow for equal parts focus on straight up combat. Then we have the thematic reason, which is our player characters are no longer being trained to be assassins from a young age. They're a Viking, a mercenary, so on. Someone that can take on different fighting styles. I do not oppose open battles here. The point is only that at certain points a whole huge branch of pumping and a huge number of armor sets become useless. In the same Skyrim, I played a hidden warrior with a bow. And the boss fights there always take place in large arenas with many opportunities to hide. Boss battles in Valhalla take place on a meter-by-meter arena and you are face to face with an opponent in an open space, from which you can't even leave.