The requirements have the form of "In configuration <XYZ>, the stick force curve must have a stable slope at all speeds within a range which is the greater of <range definition> above and below the trim speed."
It is this linear stick force curve requirement that was failing that MCAS was implemented to address. The airplane is still aerodynamically stable.
https://www.law.cornell.edu/cfr/text/14/25.175
The requirements have the form of "In configuration <XYZ>, the stick force curve must have a stable slope at all speeds within a range which is the greater of <range definition> above and below the trim speed."
It is this linear stick force curve requirement that was failing that MCAS was implemented to address. The airplane is still aerodynamically stable.