Every fanbase is a culmination of all the humans involved, so yes JK Rowling can't single handedly ruin Harry Potter... I guess..
....but no if we want to keep Harry Potter there needs to be a public, explicit reckoning where JK Rowling is literally removed from the copyright and at least some queer writers are directly empowered near the top of the franchise to run it.
Anything less is unacceptable and unfortunately I do not think we will ever get anything near that.
The only other options are to create a culture of "aggressive" fanfiction that fans begin overwriting the "official" transphobic canon with as a form of mass copyright infringement (A sort of "Martin Luther" approach if you will) somehow or to cut our losses and begin pouring love into a new fantasy wizard world that isn't owned by Queen Transphobe herself.