Hard to optimize multiple sites?

If you handle multiple sites like we say three? Five? Ten? Or more? Can you handle all of them through search optimizing? We'll I think it's very challenging and complicated as well. Why? If we pay their web hosting monthly like we say BlueHost, and to optimize them in many niches, it's quite impossible to handle it by just one person. You need a team of at least five or more people to do some search optimizing, or even hire them as virtual SEO assistants for a long period of term, only if your budget fits. As for me, I rather stick to just one or two sites to manage as it may still balanced my search optimizing schedule.