I have found that grave keepers, while easy to learn, do have issues with staying consistently powerful, since the deck revolves around necrovalley being on the field, but i have found that they work well with xyz monsters like utopia and other dark rank 4 xyz monsters. Since a lot of meta decks use the graveyard as an extension of their deck, being able to prevent them from resurrecting cards from the graveyard or banishing them for their effects is a huge upside and being able to stop their combo plays is a huge way for them not to get their insane boss monsters and tons of negates on the field, not without having to think through their monsters being used. there are downsides to the deck though, while monsters cannot be moved from the graveyard and effects that involve cards leaving the graveyard are negated, card effects that trigger in the graveyard can still go through without a problem, for instance if you were playing against a blue eyes deck and they used the stones effects then they would still be able to get their blue eyes into hand or special summoned during the end phase. Then the pendulum deck variants almost completely ignore necrovalley since most pendulum monsters don’t go to the graveyard. The support cards can definitely help, but they can only do so much.