[tripleSex]

I utilize the 'select/highlight`–'search web` flow numerous times throughout the day. I am on iOS and, like you, was unable to force the 'search web` highlight selection option to default to a non-Safari browser. However, I use the functionality you speak of through a different invocation: 'select/highlight`–'define`–'search web`. Interestingly enough, this procedure — once a non-Safari browser is set as the default web browser for the iOS device and/or the specification of preferred search engine — redirects towards the user's browser (as well as search engine) of choice. I shall investigate these functionalities' behavior on macOS — id est, desktop — tomorrow possibly and will get back to you noduerme. {Edit: deletion: " . . . ~such~ redirects . . . "}