In my experience with several large-ish companies (ymmv with smaller shops), they paid outside SEO firms good money to provide "good" SEO and tell them what we

In my experience with several large-ish companies (ymmv with smaller shops), they paid outside SEO firms good money to provide "good" SEO and tell them what we (the technical folks) already knew. However, the value was that then we were given budget/time to go make the changes/cleanup the pages/etc... And it gave weight to our suggesting that maybe not all the content should only be showing in fancy JS driven modals, etc... They also had some metrics and advice regarding the most useful keywords/content we should be utilizing (helpful stuff) that the internal marketing folks had no ideas on. Thankfully, I haven't worked at a company that hired a "bad" SEO firm, yet.