Yes, there is a difference. The TV app on the ATV will offer up suggestions and link across many different apps that are available on ATV, not just channels that you purchase from apple. The TV app that was just released for newer smart TVs only allows you to watch iTunes content through the app as well as the channels you pay to subscribe to through Apple (HBO, Showtime, etc.). Both ATV and the TV app allow Airplay 2 so no difference there. ATV has many apps as a lot of developers have created tvOS versions of their iOS apps. Also, with a dedicated ATV device you have single sign-on to your TV provider which then authenticates across many of the apps you install on it. See the article below for a summary on their recent announcements.