This claim is wrong. It’s not about sabotaging competitors, it’s about being afraid that your competitors would steal your IP they gives you an advantage.

Every Nvidia and Intel competitor (AMD) is probably already reverse engineering their binary drivers and binary libraries trying to steal their IP, so Intel and Nvidia’s fears are imo justified.

If NVIDIA or Intel could easily protect their open source code from being stolen from AMD, the story would be different. But you can’t prevent somebody from reading even GPL code, being “inspired” by it, and writing something different enough that does the same thing with the same ideas. Like just look at the LLVM project were people look at what GCC code does every now and then for “inspiration”.