Maybe I'm missing something, but how would GTA6 source leak really harm Rockstar? I mean it's unlikely it would be possible to compile a full working game from the leak, and even if so, it's such a non-trivial task, that I don't believe it would hurt sales /that/ much.
The only thing I can imagine is the story would get spoiled on the internet, but that's about it.
I may be misremembering a drunken conversation with a developer but IIRC the root cause was choice of cross-platform APIs available in early 2010s & the JSON file was tiny when introduced.
The problem was not in delivering JSON. There were better ways, but it was good enough.
The failure is that loading times had been a complaint for years, and nobody involved lifted a finger. It would be impossible to use the platform without feeling the pain.
I would speculate that it’s not about individuals compiling and playing without paying, but that with access to the codebase, creating cracks and online cheats would be trivial, which might actually hurt their bottom line
It'd make it a pain to stop abuse of their online platform when it launches, which is financially problematic given gta 5 online made rockstar billions.
If 6 leaks before release, though, that's a completely different story. I can imagine them actually paying a ransom if that happened.