I think the main difficulty is twofold. First there's the box model, which was different in IE than in the rest of the world for a long long time. Juniors that don't understand the difference will produce markup and styling that work in one browser but not the other. Absolute positioning is way more sensitive to the box model than other kinds of layout.

Second, unless you really want to insist on absolutely positioning everything, you're just going to need elements to flow occasionally. Most devs just aren't going to get a granular enough understanding of how absolute, relative, and fixed positioning work to where they can mix up the two to form fluid UIs.

They'll make one mistake and not realize it and before you know it behavior starts an inexorable slide in sanity, from which the only recovery is to scrap the entire page and start over. Been there done that.

Agreed it is no panacea. I still feel it is much more sane than most alternatives I've lived through.