Specs are useful when written by authoritative people and with specific goals. You need specs to solve issues like interoperability, defining metrics so that all stakeholders are aligned on what was built (or what is going to be built, as is often the case).
When specs are aimed at some political agenda, then Linus’ point is relevant. I guess in this industry, specs have often being driven by political agendas rather than solving particular problems.
More on this topic: Linus Torvalds Outburst Sparks Fierce Debate: Does Open Source Software Need Specs?