I agree with you that there is a learning curve and I certainly was not a pro in those days (still am not). However, I want to point out that the so called pros were wiped out big time. If you have not read "McMillan on Options" by Lawrence McMillan, I highly recommend this book. In it he describes pros that were in love with selling way-out-of-money options collecting pennies most of the time, maybe even 99.999% of the time. Then the 1987 crash occurred wiping this happy crowd of penny-diggers
As to the 90% statistic, you are right, mostly because inexperienced options traders tend to buy far-out-of-money options because they are "cheaper." The more profitable strategy is to buy in-the-money or slightly out-of-the -money options but this approach in the eyes of "speculating masses" is more "expensive."