The goal of SEO is to get a web page high search engine ranking. The better a web page's search engine optimization, the higher a ranking it will achieve in search result listings. (Note that SEO is not the only factor that determines search engine page ranks.) This is especially critical because most people who use search engines only look at the first page or two of the search results, so for a page to get high traffic from a search engine, it has to be listed on those first two pages, and the higher the rank, the closer a page is to the number one listing, the better. And whatever your web page's rank is, you want your website to be listed before your competitor's websites if your business is selling products or services over the internet.
I understand that some SEO agencies and departments are not built for the big SEO campaigns. Strategic work takes time, and speeding (or scaling) through the development stage will likely do more harm than good. It's like cramming for a test — you're going to miss information that's necessary for a good grade. It would be my pleasure if this post inspired some change in your departments.
Lastly, it's important to remember that paralysis by over-thinking is a real issue some struggle with. There's no pill for it (yet). Predicting perfection is a fool's errand. Get as close as you can within a reasonable timeframe, and prepare for future iteration. If you're traveling through your plan and determine a soft spot at any time, simply pivot. It's many hours of upfront work to get your strategy built, but it's not too hard to tweak as you go.