The answer is maybe, it will depend on how competitive the sector of your business is. Eg: If you have a business in a fairly common sector where there are lots of other companies in your area, the likelihood is you will need SEO and social media to propel you to page 1.
If your business is one of a few in your sector and area, maybe you will not need to do a lot of marketing, if at all.
Having a semantically correct, high-quality web design service is the absolute foundation to build upon. Once this is complete, things can then expand on to SEO and social media if required, which will provide brand awareness and search engine visibility.
Using a website builder without the knowledge of websites, or a very low-quality web developer to build a substandard website, is a recipe to fail online.