Let say there’s a system that is so good many claimed it’s the
holy grail, and many people are trading this one system. Is it possible
to affect the market or is the market so huge it wouldn’t matter?
The holy grail is not a system. The gholy grail is your trading plan that allows yo be profitable in the long term
A good system gives you entry and exit signal with a low risk/reward ratio and a high win/loss ratio. It doesn´t matter that a lot of people trade this goos systems. The only people that will make money are the ones that have the best trading plan.
In my opinion the answer is no. Even if all the retail traders came together it would still be just a blip on the screen compared to the money that moves these markets.