Whether or not you need a primary website in addition to your landing pages depends a lot on your business.
If you’re promoting one-off events or products, it may be the case that all the information you need to tell prospects will fit naturally on the landing page for each one.
However, if your business depends on building long-term relationships with customers and promoting a suite of products/ services, you'll probably want to have a primary website in addition to any landing pages you create.