The suspense in the film is so non-existent that you kind of feel like you are watching one of those Russian TV melodramas.

HAHAHAHAE. I have a hunch what you are talking about.

father Eric Banana

I see what you did there!

The Dassler character realizes that he loves her, or something, and decided not to kill her. So he just leaves her there on the lake alone.

That's it? My Michael Bay mind is mushrooming with possibilities of what cool action scenes can be done. Or at least some suspenseful drama.

If I would have written it, I would have revealed that Sylvia Hoeks character is a part of the cult, and then not make this information known to the father until the very end. This would create a lot of cool irony. And automatically will make everything a bit tenser. And then not make Dassler character leave her there alone. But instead maybe just make him hesitate longer, to win some time for the plot to get to the point, where the father has to confront him. And at this very point, we already know that his "friend" Sylvia Hoeks character ( who is a cop, and therefore has a gun ) is on the side of the bad guys. Which creates a hell of a tense little situation.

That does sound more interesting. As Robert Mckee observed, a good plot is everything. Or so I recall.