Katakuri hasn't openly defied his mother and I doubt that he would ever challenge her, he is fully aware that she is much stronger than him and that challenging her could cause a civil war within his family and he certainely doesn't want to see his siblings fighting each other and having to hurt them, not all of BM's children are loyal to her only out of fear and most would side with her than with a losing party.
Also Big Mom would certainely not leave Totto Land defenseless, she isn't crazy or stupid enough to leave her kingdom without a good portion of her crew to rule and watch over it while she's away.
And for someone who doesn't take failure well she isn't completely ruthless as she still kept Snack alive and well despite his defeat against Urouge, didn't punish Tamago for having been bested by Pedro and took with her to Wano several of her children that failed or were beaten during WCI arc.
So I do not believe that she discarded Katakuri, Cracker and the others.
And I do not view her as a psychopath either, she has traits that psychopaths do not have, and this term is too quickly and easely used to categorize characters without knowing what is a psychopath anyway.