Adobe XD is a collaborative tool for prototyping and publishing websites and mobile apps. While it’s vector-based and involves considerable design elements, it’s not, first and foremost, an art creation tool.
Adobe Illustrator is a vector-based design tool meant for creating illustrations, logos, icons, and typography, but it isn’t ideal for building a website from the ground up. However, files from Illustrator may be imported into Adobe XD and edited for publication.