WordPress.com has a relatively expensive hosting plan for sites based on the WordPress.org version. I know of one site using that solution, and it was because they trusted the WordPress organization. Not really different than most hosting companies – just WP.com instead of SiteGround, GoDaddy, etc.
But you cannot have a WordPress.com site that uses most of the themes available on WordPress.org. There are a few that have made the transition to WP.com, but not many. It very very difficult to get a WP.org theme modified and approved for WP.com.