The only thing this tournament has shown me is that there probably isn't as clear cut rankings to ODIs as I thought. I would have said Aus/Ind and SA were probably a tier a head of the rest but I think like with Tests there appears to be a top 4 with some difference but not a great deal.
Lack of great teams currently, just a few very good ones with flaws. Makes it quite exciting in all forms to be honest.
Rankings are based for major part on bilateral series, not one off games. The best team will not necessarily win a short tournament of this nature where you have one bad game and you're almost out and in LO cricket, on a given day, anyone can beat anyone. Let's look at some of the surprising results
Pakistan beat South Africa (but won't win against SA in a bilateral series home or away)
Bangladesh beat New Zealand (but won't win against NZ in an away bilateral series)
Sri Lanka beat India (but won't win against them in a bilateral series home or away.
Even Australia losing to England, while not an upset but you can't really predict the winner in a 5 match series. Australia is a quality ODI side and their performances over the last 2 years should get more weight than 1 bad match.
So rankings can just give us an indication of pre tournament favourites but once the tournament starts, it really is anybody's game.
Australia, South Africa, India and England are a touch above the rest of the teams.. That still stands even if 3 out of those 4 teams get knocked out in this tournament.