Honestly when you said seeing results changed your view, I get it, but I've had the opposite happen. I exposed the root flare on a maple like everyone says, and the thing just dried out and struggled in our hot summers. Sometimes that extra soil depth seems to help with moisture, at least where I live. Maybe it's not a one-size-fits-all rule, @dakota_rivera.
The Morton Arboretum website has a detailed guide about root flare exposure. It explains that trees planted too deep often develop girdling roots and struggle to establish. I read that guide a couple years back and it totally changed how I plant trees. A certified arborist in my town said most landscape trees die early because of deep planting. Seeing the root flare lets the tree breathe and stops moisture from building up around the trunk. It's a simple step that a lot of folks overlook, but it really helps trees live longer.