Strange I've been a controller user since i started (playing on ps3 and then eventually ps4) and I've never had an issue with the soft targeting. It's honestly the best thing ever in terms of healing, for me at least. But then again I usually have a trigger held down constantly as soon as i enter combat, on all my jobs.

I don't honestly think there's a way to disable it.. I've dug through the options and can't find anything.. unless I overlooked it.. Odd though, as thorough as they are with giving options and customizable settings, they do miss a lot of little things, like this.