Well, east blue probubly produces the fewest strong pirates. However, the few that do come out of there who are strong are usually REALLY strong. So that statement can still be true given how few strong pirates emerge from there. I think also the total bounty on all pirates in east blue is smaller than any other ocean too.
Side note too: Thinking about how big the bounties on each pirate is and given how many pirates there are out there, if every single pirate were turned in for the reward money, the world government would go broke.
However, I do suspect that the world government sets those bounties only expecting to pay out on maybe 1% of them. The rest they expect to never have to pay because the pirates will either never be caught or someone (be it a marine or another pirate) will kill them off in pursuit of that bounty.