I think they are. At least, I have never been disappointed in a GKIDS edition . The GKIDS discs have new transfers and new Gibli-approved subtitle tracks, and some of them include additional bonus features (presumably from the Japanese editions) which Disney did not include on their editions...
They are the same discs as GKIDS previously released. They have done this a few different times this year with other titles as well. I bought several Gibli titles on DVD back when the rights were with Disney. Then I upgraded them to Blu-rays which also came from Disney. Then I upgraded them...