Regardless of Flash's test screenings, it's a bad look to keep Ezra but ditch Gal .
I don't know if Flash is as good as insiders claim it is.
But even if it is , to keep them , Ezra, after all this turmoil ,but ditch Gal and JM's Aquaman is gonna be hard to justify regardless of how good or bad Flash is.
I didn't think the hard reboot of the entire universe was all that practical at this point and time anyway, especially since the rest of the slate hasn't even been released yet.
So the idea of potentially keeping the characters who went over well, and ditching those who didn't , I could see happening.
To be fair to Gunn, he never has confirmed that the whole universe was going to be rebooted .
That's been more an assumption of scoopers , the geek pundit community, and fandom.