I would say that sports betting is both skill based and luck based. It depends on how much time you put into researching teams, players, coaches etc. You need to know the sport inside out in order for it to be successful. The more research you do before placing bets, the better chance of winning.
If betting is a skill, it would have make many gamblers a millionaire today, and many gamblers would have like to be using any amount of money to gamble because they know they are going to win anytime they play. If you are skillful on a particular thing, you will not be afraid of losing because you have the skill to know the final result before the end of the betting.
I guess betting is a luck, what you are not expecting from your betting can come to you to be happy or sad at the moment, which is the reason gamblers should gamble wisely for them not to be addicted to gambling.
If you believe in luck you ought to play casino games.
Sport betting is the only kind of gambling where you can decrease random. And you prefer to believe in luck - increasing random. It is silly as for me - to play predictable game and believe in luck the same time.
In sport betting the main problem is high quality analyze and discipline. You have to control your bets, odds, the size of bet, bankroll - it is serious job that common gambler don`t like. That`s why you don`t see millionaires around you.