Yes, you are right, it is very expensive for the broker to have FCA or any other huge regulation. This brings the trust into it, and more clients obviously.
One of the things that regulated broker can do is to slow down the execution of the trades with couple of seconds maximum. How ever that is a problem for the scalping trader, or for the EA trading on M1 chart.
That is one of the reasons I choose M15 and higher time frames. Yes I use M5 and M1 but with higher time frame filters, so even having a small delay wont effect the trading.