The time when game sources were a major competitive advantage ended roughly around the start of the iPhone era, not just because of more source availability but also a shift towards cross-platform maintenance, live support, and high fidelity assets as the things that distinguish large productions.

Like, you still get "asset flip" games that copy default projects, but they are background noise. Having the source to something large like CDPR's games doesn't mean you have access to the studio infrastructure of CDPR.