As numbers of visitors from search engines drop, that site will be losing traffic. That is too large a figure to ignore. Sure, a high-profile brand like Amazon will have higher numbers of direct URL visitors. You are totally correct about the difficulties of search engine rankings. Yes, the goal posts are always moving.
Most companies use professionals the whole time, for accounts, graphic design.
A professional e-marketer is constantly reviewing how search engines are checking submissions. They understand how to make the best submission to each individual search engine. Good ones will do submissions manually, optimized to each search engine. Only in Google did I get the Sotheby's banner. This has no relevance to antique cars at all.