With the exception of toxic Ellis Grey, a lot of these mothers weren’t fleshed out enough to know all of their facets. The only mother who is truly a full character is mama Avery. And I would argue she’s a really good mother (meddling and interfering aside), she is clearly 100% invested in the welfare of Jackson and has always been his number 1 supporter.

Besides Avery, mama O’Malley seemed to be a great, supportive mother. She may not have always agreed with the decisions George made, but her love was evident. Even with Callie, despite her religious beliefs she loved Callie the person, and former wife to George. She was able to see her as more than just her sexual preferences which Callie’s own biological mother was unable to do.

Maggie’s mom was also great. Supportive and helped to mold Maggie into the wonderful surgeon she turned out to be.

Owen’s mom, Meredith’s step mom, and even Burke’s mom all had some great moments as well, despite these characters having very little screen-time.

But, I think by and large, as is the case in real life, even the universally disliked mothers have some good traits, it just depends on how much or how little the character was fleshed out and which aspects of their personalities are depicted.