The (super) glue sucked into the porous rail of feather fletch, liquid and gel, got into the lower part of the feathers and welded the feathers and impeded some of the flex
I have fletched hundreds of feathers with Goat tuff and even crazy glue and have never, not once had any get into the feathers.
I can understand your quest for a better glue, but don't understand how you get glue above the base and into the feather.