I personally think another parent figure to act as a brake for Fran is a nice addition to the story since:
1. Fran is already talented and adding sword dad makes her even more stronger than it should be
2. Sword dad won't be getting in Fran's way since he admits later that he's not only Fran's guardian, but also Fran's sword so whatever she decides he'll protect her to the best of his abilities
3. Neither of them are well versed in this world because sword dad is an isekai MC and Fran is just a child, and that can lead to an early grave