This I know. And that a soulgaze is an application of The Sight.
Yes, likely just so – but I think it is important to remember that the Sight (third eye) and a Soulgaze provide different information (and to me they seem like they do). Much like the difference between a sit down visit and exam with your doctor vs. an MRI and a battery of blood tests. One may reveal a problem that the other cannot, but then there are times when both will bring forth information about an ailment. And then lastly there are times both might miss something.
To my thinking a Soulgaze is like an MRI and blood tests - more internal focused. The doctor exam is a more surface examination like the Sight.
For example:
If in Turn Coat Harry had used his sight on Morgan, Harry would have noted Morgan’s aura as a wizard, seen some manifestation of the summer cloaking spell that was keeping Morgan untrackable, and perhaps the remnants of the spell(s) and funny ink that were used to set him up. Harry would not have gotten any kind of good read on if Morgan was telling the truth or not.
If Harry had soulgazed him he would have had a read on Morgan’s general personality and current trustworthiness… not a perfect read of course, but still a generally useful bunch of info on which to gauge Morgan. I don’t think a Soulgaze would have shown Harry the Summer cloaking or anti tracking spell.