Just because you have not seen it doesn't mean that people have not achieved such results in sports betting. They are actually both risky. Combining too many games on a bet slip isnt really a form of any strategy it's the same as just relying on luck and that's the same thing with aiming for a high multiplier in casino games. There's nothing wrong in both of them as long as you always stake low
Both ways to gamble money are pretty risky and it is almost a guaranteed loss for anyone who dares to wager a significant amount of money. The most important difference lies in the fact it is much more fast paced to wager on slots than going for parlay, and thus it is more likely to lose money from playing slots than doing it through parlay. It is just a matter of pressing a button, it is not the case with sport betting, in which there is more time for us not to get our mind fogged by greed and run after losses.
Also, Those high multipliers are on iously intended to be played with a fairly low wager, but there will be always people willing to risk more than they can afford to lose, for the sake of money.