Adjustable Objectives are definitely going out of style, or already have. For me personally, I haven’t bought an AO optic in probably 15yrs or so - when I was shooting Benchrest and F-class, AO was fine. Set the parallax and get behind the rifle, because the targets are at one distance. For BR or F-class, an AO does have the advantage of finer control, turning a larger “knob” instead of a finer one.
For any kind of field shooting, side or top parallax is favorable. Parallax can be adjusted more readily from behind the rifle when shooting SF. I can REACH my AO’s to adjust, but I cannot see the markings to get into the right adjustment without breaking position from behind the rifle. Side focus or top focus is an advantage.
I don’t agree with the premise that AO’s can be set and left alone while SF must be set for every shot. Either can be left alone or adjusted, but it there’s nothing really about AO which prevents parallax errors when the parallax setting doesn’t match the actual shooting distance. As an example: I rarely ever adjust my parallax during a stage, despite potentially shooting 300 to 1000yrds all within the same 90 seconds, and despite having visibility of my parallax and a quick spinner handle to facilitate adjustment. I’ll set my parallax for the longest range and shoot the shorter targets without issue.