Lin Fan didn't have any fear that the four sects would be weakened because of his actions.
Since they were weakened, they wouldn't be able to fulfill their roles as cannon fodder as well as if they were as strong as they were before. As such, it would mean that the mission to subdue these sects would only be considered a half success.
Still, Lin Fan didn't care at all about this.
After all, he knew that the most important thing was loyalty.
It didn't matter how strong they were if they were disloyal since all that it would mean is having another knife in the dark to look out for. It was better to just snip their wings and train them to be loyal pets than to leave them as wolves that could betray them at any moment.
Just because someone gave them a piece of their soul, that didn't mean that they would be absolutely loyal.