These three could do so much better on their own, not working for team rocket.

Hell, if they wanted to go legit and just start being normal pokemon trainers, they could easily take the pokemon league by storm.

Unfortunately, they will never decide to quit team rocket and become Ash's travelling companions, even though they could easily; Pikachu keeps trusting Meowth no matter how many times he stabs them in the back, it can be assumed that Ash would trust them too.