to be competitive with others margin should be way lower than 5% , it's really high and not acceptable
I do gamble every day on sports and I can tell you having a lot of markets to bet on isn't my concern since over 90% I just go for ML , Handicap and over/under
I only use bitcoinrush , betking and sportsbet so it's all about the odds not about the markets available

sportsbet has high margin but they also have price boost where bettors can get odds higher than anywhere else ( even fiat sites ) so IMO sportsbet still way better than betcoin

I hope you consider improving the odds cause such threads will make people realize where they should bet and I would say no one will be using sites that have high margin