Placing your support hand UNDER the gun hand is the old "cup and saucer" technique.
It was lacking then, it's lacking now.
When firing single shots or slowfire, then technique doesn't matter as much.
There are pictures of Elmer Keith firing a .44 magnum in full recoil that show his hands totally separated by the recoil force. For SINGLE shots, such as when hunting, this doesn't matter one whit.
For accurate RAPID FIRE, such as when shooting to defend your life, it matters a lot.
A good, properly executed technique allows the gun to be controlled during rapid fire. (We'll define rapid fire as 1 shot per 1/2 second or faster)
If your technique or execution won't allow that, then keep looking or tweaking.
.