The story of Shambuka is thought by many to be an unreliable interpolation within the Ramayana. And even then, Shambuka's violation of dharma is said to involve his improper performing of tapas, a kind of ascetic penance that's often criticized in both Buddhism and Hinduism; certainly, it's not considered universally good. It's not to be confused with meditation or reflection in a general sense, of which we are even told wrt. the Shudras that live in the forest (i.e. pursuing Vanaprastha).

(To top it all, apparently there's even a tradition which says the wise Shambuka ultimately managed to perfect his dharma by means of Rama's intervention, whilst the Brahmins who had requested that very intervention are criticized. Thus adding all sorts of nuances to the story that can hardly be described as "casteist".)