I don't think it is fair to discriminate these pokemon just because of their stat total. Base stats are not everything- it is chiefly how the movepool and typing matches their stat distribution that potentially makes them game-breaking. Just look at Infernape. His attack, special attack, and speed are perfectly balanced, making it a popular mixed sweeper with a relatively low base stat total.
Celebi is hurt by a serious weakness to bug moves; Tyranitar suffers from a fighting weakness, and the dragons suffer from ice moves running rampant in the metagame.
We need the variation offered by 600 BST pokemon. They are pretty much the definition of bulky sweepers, and the metagame would become unbalanced if we removed them.