There are better options for P2W, but he is probably the best a F2P player can get right now. I've been using him for quite a while now, and I can tell you Itachi Edo is a good counter to him, but mostly because he dodges chase and cuts nin damage. You can reach up and kill ~50k power higher than you with a good grudge team. But don't expect him to solve all your woes. The key to grudge is he can buff huge first round. But if you haven't won by round 3, then Kushina or Minato might have grown to be his equal in damage dealing and will just keep growing. He is also very helpful in ninja exams. :)

Kakuzu's bonus isn't a "buff" that can be removed. Preventing chakra is the only way.