@wpsmort Wholeheartedly agree with @zanami, overriding an existing plugin’s behaviour is not an acceptable practice, and is somewhat against the spirit of the repository guidelines (9).
A better practice would be to simply offer the user a choice to disable either the XML Sitemaps Plugin OR the XML Sitemaps Feature of AIO, and provide direct links to both of those actions in the admin message.
A more complete practice would be to detect which plugin is the newly installed one (via the WordPress installation hooks) and set the default behaviour according to that until the user sees the message and makes their own choice.
On a positive note, I love the plugin and always have, and this situation led me to finding the Feature Manager so I could disable the feature until I can determine which plugin is better suited for each client’s site… and in doing so I see a whole bunch of other cool feature extensions I didn’t know about and need to look into! I think you could definitely make these easier to find, and announce new features like this better, as they look really useful (I couldn’t even find instructions in the documentation for turning XML Sitemaps off anywhere.)