Kandi Burruss -- Kordell Stewart is Fumbling Facts About Porsha Williams' Mothering Skills

Kandi Burruss is sticking up for her "Real Housewives of Atlanta" castmate ... saying she highly doubts Kordell Stewart's claim that Porsha Williams is a stepmomster from hell.

TMZ broke the story ... ex-Pittsburgh Steeler Stewart ripped Porsha in divorce docs last week, accusing her of partying all night, disappearing for days, and neglecting his son.

But at LAX, Kandi told us Porsha "never really did anything unless [Kordell] was comfortable with it."

She also told us Porsha's the one who sacrificed -- and you gotta see the dig she gets in at Kordell's expense.