If the ratings were accurate - eg even money means winning 50% of the time, then getting 2/1 on an even money chance should return a solid profit on turnover.

Eg on 2 $100 bets you outlay $200 and get back $300 for 50% POT.

What it shows is that the ratings are inaccurate. I reckon some pricing services (all?)probably deliberately put prices short so they can claim an 8/1 winner rated 2/1 etc..