What I'm basically saying is it doesn't matter if it's forced. They're main characters, and deserve their appearance, even if it is only a token appearance.
Characters don't 'deserve' anything. They're fictional, and as such have no actual rights. If a character's inclusion in an episode does not add anything to that episode's plot but instead only wastes time that could be used better, or worse, actually derails and hurts the plot, then it's better that said character not appear. Mallow's episodes often suffer precisely because the writers choose to force Team Rocket in there.
I believe that forcing such a rule constrains the writing potential and plot too much for the sake of... I'm honestly not sure.