Doesn’t it seem odd that we need PHP for this?
Intuitively, if I don’t want to use the standard page template, I am going to be clicking the “Edit with Bricks” button in the page editor (like, isn’t this how Elementor handles it? Trying to remember…).
The default should be just that, the default—but then if I choose not to use the default (ie., hand design that particular page in Bricks), then that very action of clicking “Edit with Bricks” should override the default—it’s implicit.
Bricks could add a warning like “Hey this is going to override the default page template for this condition - are you cool with that?” if they wanted to.