Apache 2.0 is pretty good. If your business depends on no one forking you, you are already toast.

The worst case scenario is a really competent team out executes your idea. They are not going to be stopped closed source. But if your code is open source to begin with, the market rapidly fills up with forks covering every application niche.

This actually makes it harder for a competent team to enter and execute, because now they need to beat N other teams.

The first to implement and brand the idea tends to win the dominant share of the market, unless they fall asleep at the wheel.

IMHO, OSS accelerates pmf and tam, and as an investor the highest ROI is in products that win dominant market share despite being easy to fork. That means their moat is established and hard to crack.