Do ratings help to decide a Wrestler can draw or he is over with the fans ?
To a certain extent. But actually, MONEY helps decide whether a Wrestler is a draw. How much money does he or she make for the company. Television rating has its limitations, especially in the internet age.
This is one reason why I think often critics go too far in the comparison to ratings under Punk and ratings under Diesel/Nash. When Nash earned the nickname "lowest drawing WWE champ in history" it wasn't just that TV ratings were down. Also, house show attendance was down, with arenas being half full, sometimes less, merch sales were down, PPV buys were down. Business all around was down. (To be fair, much of that was not Nash's fault, but problems he inherited from the previous generation, fallout from the steroid trials, top talents leaving to WCW, etc.)
But under Punk's reign, business is not anywhere near what it was under Nash (even when accounting for inflation), in fact, business isn't down at all under Punk. I think that's what many critics of Cena & Orton miss as well. TV ratings have been consistently going down for the past 6 years annually, yet many of us were mind-boggled as to why Vince kept keeping the belt on Cena.
Because Cena makes money. Without money, ratings don't mean shit. That's one reason why Stacker 2 dropped WWE as a sponsor. Yes, ratings were high at the time, but Stacker was not seeing an increase in sales after airing ads on WWE.
Same with being over with the crowd. Doesn't mean much if they won't pay to see you at house shows or buy your merchandise and PPVs.
What WWE wants wrestlers to draw are $ signs, not Nielson points. Ratings are just one aspect of measurement, and that by itself is not reliable data.