There are a few reasons why this hasn't been used.
First, as has been mentioned, the air loadings tend to make the surface deflect more.
Second, if there is even the slightest amount of slop in the system, since the control tends to deflect, you will probably be hunting around neutral. In inedxperienced hands this could lead to an uncontrolled porpoise.
Third, I have used the full flying stab before. Works fine. You do have to be careful on the pivot point. As I recall, about a quarter of the way back is a good pivot location. It could be that your friend had the pivot point too far back.

The T-tail plane you mention, there are reasons why you do not see vary many of this configuration. First, the stab is in an easy-to-break location. Next, the T tail configuration tends to barrel roll. As the plane rolls about its longitudinal axis, the stab moves in a circle, scooping air as it does causing the barreling out of the roll. People prefer a plane that looks nice in a roll so 99% of the planes don't have them. The T-tail does get the elevator out of the wing wash, making is more sensitive than a conventional tail.