Invokeds and dark magician are actually winning the tournaments against this deck.
There's no reason to limit it, it's a balanced and healthy archetype.
No one said anything about limiting Shiranui. What they want is limiting the grass, as it gives too much advantage for a first turn. Lightsworn, infernoid and such would be broken as well with this card on their first turn
Like any deck, if you get a lucky play you'll win, and if you don't, you'll lose. I've beaten plenty of grass decks with Cyber Dragons (and lost to plenty of them too). I haven't felt like they were too OP compared to other archetypes (looking at you, Darklords).
No deck will ever be as abused as when Sylvians where originally released. Self-milling your entire deck to nuke the few cards your opponent had and proceed to fill your entire board to sweep for game.
If Invoked, Dark magician and Shirainui decks stays unlimited then Konami should also unlimit Amazoness decks.
According to the replays posted in the new unlimited cards mode, even unlimited Amazoness decks get slapped really hard by those 3 decks with limitation.