Galad can channel!!

There was virtually no chance that such news would immediately change such long held beliefs, particularly when abandoning those beliefs would endanger one of the pillars of Seanchan strength.  May things change over time based on this new knowledge (if it even WAS new knowledge)?  Quite possibly.  Were the Seanchan going to immediately release all their channelers?  Absolutely not.  It would take away too much of the Empire's power and its unrealistic to think they would do that even if they absolutely believed it was the right thing to do.  Beyond that,  most of them don't even *want* to be freed.  They have been thoroughly indoctrinated to believe that they are too dangerous not to be kept on a leash.  What might happen is over time Tuon can be convinced that it is in the Empire's interest to train rather than enslave channelers.  I suspect if that did happen though,  Empire trained channelers would not swear the Three Oaths of the White Tower, but just one Oath....fealty to the Empire.