@OP I do not think you can compare the odds of coin toss and sports betting. Coin toss is obviously a chance/luck type of game while sports betting is more inclined on the skill of the bettor. So integrating the possibility of a coin toss to support the argument of why 90% of bettors lose in sports betting is somehow moot, IMO.
It is true that most gamblers who like to bet on their sports do not have extensive knowledge of the sport at stake and some gamblers are only fixated on the odds of the betting options.
Actually this provides a bigger risk but unfortunately no one cares about that and only thinks about the chances of winning.
It is the choice of the gambler to bet even though he has no knowledge prior to the sports he is betting. A more responsible gambler will often consider their knowledge regarding the sports they wanted to bet. So this only means that most gambler that bet on sports that they lack knowledge thinks that sports betting is a chance type of gambling games which we know that is not the case.
It is true that the more research that can be done on sports betting, the higher the chances of winning can be found. But there is no guarantee. Many may object to this because there are instances in sports betting where a team has a 99 percent chance of winning but still loses. No matter how good the team or how good the research, good research can become worthless because there is no guarantee of victory. So there is no option to give equal importance to luck along with research.
The knowledge itself is the guarantee that a bettor have higher chance of winning. Though there are upsets but that rarely happens compared to the team that has an actual advantage of winnings.