Firstly, if people start mirroring your trades, that's a good thing. The extra buying power will help to push the market in your direction. Secondly, anyone that would be dumb enough to mirror another person's trades is going to go broke. What if the star hedge fund manager is using futures to hedge a share portfolio with a different broker. You copy the futures trades but don't know about the share trades. Suddenly, the you're losing a fortune while the hedge fund manager is market neutral. In practice, it's not very smart.
LOL. Unfortunately, this reasoning doesn't apply to traders who are trading with a smalltown prop firm. And I think these kinds of traders are the target group of OP in this thread.
Like I said early in the thread is I can confirm prop firms do try and mirror top traders strategies, as for the extra buying power well it really depends on the strategy and have even know a few strategies to stop working for the trader as the firm was front running them
That's the reason I'll never join a prop trading firm. I keep things more secret than the Coca-Cola recipe on my private trading server.