Almost everyone that i know who bet favorites lose long term.
But weather you are successful or not depends on if you are playing the value odds. There can be value in favorites too. But in most cases big favorites are not fairly priced and there is no value and if your strategy is always betting heavy favorites every day, then you will likely come out losing in the long run. However, if you are a value hunter who patiently waits and snipes the value plays once in a while you can make money.