Earlier quoted context omitted.
I see, I'll play around with it a little more then. The thing is that the OSMAnd route looked way worse, and from using it on shorter routes occasionally I didn't really trust it.
Yeah, OSMAnd's built-in routing isn't great. But anything based around exporting a GPX from one app and using it in another is going to have the problem you describe; the only way to avoid it is to find an all-in-one app that's good enough on all fronts (or possibly use a fancier format like TCX).
[1] https://github.com/GIScience/openrouteservice-app/pull/323