That is a completely incorrect understanding of Chevron. The courts under Chevron would immediately strike down the FDA attempting to regulate motor oil as that

That is a completely incorrect understanding of Chevron. The courts under Chevron would immediately strike down the FDA attempting to regulate motor oil as that's not a reasonable interpretation of the regulatory laws that Congress created. What this ruling changed is exactly that Congress now does need to be exhaustively thorough otherwise the courts decide the matter, not the agencies