Comparing sports betting to financial markets is an intereting topic. I will start out by saying that sports betting is able to offer a far better return on your capital when your bankroll is small but the stock market is superior when your bankroll hits the bookies’ limits.
A typical sharp might be able to maintain an ROI of 2% to 7%. Let’s assume 5% ROI. If you’re able to get about 1000 bets down risking 2% of your bankroll on each bet. You would effectively have 100% return per year. This is also without changing unit size during the year only at the end of each betting year. 100% per year is going to compound very fast so if you have starting roll of $50,000 you’re going to be at $400K after mere 3 years. If you’re betting a small market(for example a lower level soccer League in europé) you’re going to get limited and banned pretty quick by the bookie since you’re maxing out their limits each time you’re betting. Therefore sports betting get tricky when you get up to a certain amount. For people betting on NBA, NFL where the markets can absorb huge bets by sharps it’s a Little easier. I can’t give specific numbers as it depends on accessibility to betting and what sport you’re exploiting but whatever you’re betting on you’re going to have a ceiling which doesn’t in practice exist in the stock market. You can easily dump $10 million into a index fund get an average return of 9% per year without getting told by the broker “sorry, you’re only allowed to invest $100k”.
If you’re investing in a passive index fund, you don’t need to spend any time analyzing or checking your investment while sports betting is going to require active participation. Active trading compared to sports betting is a little tricker to evaluate but generally speaking you’re not going to be able to obtain 100% average return in the financial markets without running a very high risk of ruin while in sports betting you can implement a low risk of ruin bankroll management and still be able to obtain 100% or even more in average bankroll growth per year.
To sum it up: with a small bankroll sports betting offer far superior return(assuming you’re a winning a sports bettor) and with a large bankroll the stock markets crushes sports betting.