Mrs. Matthews and Morgan were weak characters
I know they're supplemental characters, but in the great shows (Fresh Prince, Family Matters), those supplemental characters add a lot. Mrs. Matthews and Morgan didn't provide any laughs, and they weren't the centerpieces of any major themes or storylines.
Mr. Matthews, Mr. Feeney, Corey, Shawn, Eric, & Topanga were excellent. Mrs. Matthews and Morgan weren't.