Vet its self is not the problem, they are very strong yes, but that is not a bad thing, however Kha is a massive problem as not only is it crazy strong with their main deck it is singelhandedly removing things like vaath, lancer, and artifacts from the meta creating a power vacuum being filled by things those decks usually counter, leading to a narrow rock paper scissors meta.
The problems with the game from a design perspective due to leading to toxic playstyles/warped metas are Kha, Wanderer, and Gate/Mantra. These are the least healthy aspects of the game, and desperately need to be addressed. Deci/Spikes is also pushing it but is the least offensive of the bunch.
From a balance standpoint Rag and Ziran are a bit overtuned, although if the design problems get addressed the natural predators/tech counters to the decks will return making it less bad, but they are still likely a bit to much.
Abyss/Vanar are a little behind although both do have at least a couple good things going for them, and if both the design/balance issues were addressed they would probably be fine, or alternatively leave the overtuned decks alone and give the others a small buff but either way the design issues still need to be fixed.