Well that one's easy to answer, they're either A) lying, or B) working on the simplest possible software where this kind of stuff doesn't explode. Or the alternative 3rd option of what you mentioned, the initial pre-MVP phase goes decently but then it all collapses inevitably as the slop accumulates and the codebases become unmaintainable grey blobs, but that hardly matters to them because their MVP app never makes it past that initial stage before they jump ship to a new "amazing" idea.
The lying comes down to astroturfing and shilling from the LLM companies that want to sell people on the idea of vibecoding and tokenmaxxing.