I main Tank job so that's probably not exactly my topic, but still. 1st thing I learnt as Tank as soon as I started to level my first melee job is... dont. turn. damn. mob. around. (I still wonder why no one really yelled at me when I started play the game...).
That being said, positionals is something that doesn't make the job really challengable, but does make you dependable on Tanks and their ability to avoid turning mobs. If they will be removed, the only thing that will be really gone is stress and annoyance of situations when you try to do your best but your co-patry Tank makes everything for you to fail. On the other hand it's also something what makes melee jobs different from others, and there certainly are players that would miss that if it's gone.