Where did that comment come from?
Don't know about "stronger", probably depends on the formulation used. But many find AlNiCo to provide a richer, warmer, and more musical sound. OTOH some report that AlNiCo magnets lose "strength" (flux density) over time.
Some kind of Alnico yes other no, there many types of ''Alnico''.
Alnico woofers and FR usually had more some SPL in the bass, are deeper also.
See AudioNirvana freq. Charts from the Alnico and Ferrite FR.