Lol, there's literally no way for you to be able to make that conclusion, because we have no idea what would have happened instead had he stayed(other than he would have had another kid, which, in and of itself, is already a pretty massive loss).
Did it? He gained a wife, but lost a hand and a potential child.
What if, at some pivotal point in the future, he's unable to save someone else, because he's missing a hand? It could be something as trivial as Sylphie dying because he's unable to reach out and grab her.
Or maybe beast kid would have ended up saving someone that he couldn't.
We simply don't have enough information. But you're insistence that we do is starting to border on manga-prophet territory.
But also how Beastman society works.
By having a child with one of the beastmen, he possibly would have earned the loyalty of their entire tribe. Which might have played a pivotal role in events later.