I never said they don't resist Cybele?
I'm saying any additional effects from Cybele that aren't it's petrification don't make the resistance any better than what would be considered baseline.
The point is that Cybele can affect people who would otherwise resist petrification because it has enough oomph to it. A weaker characters petrification ability would not be able to affect Merlin or Saber Alter.
There are degrees even in hax