No losses, I was practising with smaller cap before scaling up
Till date my max DD is 5% 
4 lakh not just in brokerage. 4L is brokerage + other taxes together
I agree with your valid point. one thing they can do is reduce the broking charges. It could be 5-5 for buy and sell, if traders do more activity on their platform they can earn more. win-win situation. 