They think that Linus and a few buddies could have just written an OS from scratch with no free compiler and no free buildsystem and it would have turned out functionally superior to existing Unix's.
They literally believe GNU did nothing important, in utter ignorance of the difficult of writing a free software compiler that had an acceptable optimizer from the get go and evolved into a better optimizer than all previous proprietary software and writing replacement to all of the Unix software that is also faster and more reliable.
Someone may chime in and say "but LLVM" - but LLVM could not possibly be written without GCC, as it started as a GCC frontend.
LLVM frankly should not have been written - it is the LLVM's developers duty for the sake of humanity to adopt a free copyleft like the GPLv3-or-later or AGPLv3-or-later, or find and delete all copies of it, but they relentlessly shirk their duty.
@blenderdumbass The average fediverse user can just ask what those are and they'll get their answer.
GCC was GNU C Compiler, a 100% free software compiler in the time where all usable compilers were proprietary, which eventually turned into GNU Compiler Collection, when more languages were added and upgraded to the GPLv3-or-later, when that license was released - ensuring it's 100% free software for *all* of it users.
LLVM (Low Level Virtual Machine, but they don't use that name anymore) was previously a GCC backend (I made an error in the previous comment and called it a frontend) to investigate dynamic compilation techniques, under a weak license and apple a few years later hired some of the developers to develop it further (as they wanted a functional compiler for their use without having to continue to license proprietary compilers) and paid those developers to turn it into a standalone backend and later add the clang frontend to make it a standalone compiler.
Apple also didn't really want to hire and pay for more programmers to improve LLVM, so they agreed that LLVM and clang etc (less their private modifications) could be released under a weak license, so other people could do gratis labor for them without apple having to pay.
Other companies like nvidia and AMD and many other companies saw the weak license and went "great, lets make this proprietary" and the result is a compiler that is under a free license, but is proprietary software for many, or possibly most of its users.
@picofarad As far as I can tell, such compiler was useless, as it was proprietary software (that could not have been freely distributed or modified) and it appears that it doesn't really implement C good enough for a good kernel.