First I will like to understand something becoming succeed over the long run what those that mean, is it maintenance of winning record for long term period without losing, if is that then I will say skill and luck all together because is not possible to win without losing in sport betting for a very long term the only thing that is possible is winning more than you lose, no matter the skill you have or how good you are in knowing about that particular sport you are always playing you will surely lose one day because somethings can happen that will make you lose bet.
However if by successful you mean winning more than you lose then yes you can do that by just your skill you don't need luck, there are people who just focus in sport betting and they win more than they lose, they are well knowledgeable about the particular sport they bet on, those people that feels that they can  use luck to be winning more than they lose really don't know what they are doing or saying.