"that isn't Joyce, that isn't Joyce!1!1" no that is Joyce when she's been slowly healing from feeling the weight of grief and got the love of her life back, all her children are moderately safe (or safer than usual) and she has a better emotional support net around her in general, that is Joyce trying to listen to what her son told her and change her behaviour to have trust in his ability, that is Joyce who has always also been sweet and kind with everybody but with kids in particular and she's always been deeply nurturing even when she's able to pick up an axe and put her whole body in the line of fire or against a whole ass Demogorgon to protect her children (and also not her children)
She's not "dumb" for having trust in her sons' and daughter and almost husband ability to come back to her when they've all been handling this big thing for years at this point and they always managed to handle it, plus she can't control everything and her letting go of that need to control Will and keep him safe is part of her arc pretty explicitly this season
