Anyone can do a simple evaluation to show that the tab does
not add any stability in the Kirk design.
1) Remove the bottom bracket screw so that it does not interfere with the evaluation
2) Attach the Kirk L-bracket to the camera and fasten the tab to the camera left strap hook as tightly as you can
3) You will see that the tab does not clamp on the strap hook at all and the freeplay allows the bracket can move in the x, y, and z directions at the tab position.
Bottomline, the strap tab design in the Kirk L-bracket is useless and only adds to the inconvenience of having to constantly remove and re-attach a strap, and having to lug around two different allen keys for two different screws.
I think yours must be out of spec, because I just did the exact test you propose, and got opposite results.
I left the bottom screw loosely mounted and then attached the side screw tightly. Then I completely removed the bottom screw and found that the side screw locked into the tab tightly enough to whole the entire L-bracket in place securely.
Obviously if I pulled up and out, it would come off, but it's definitely adding a lot of stability on mine. I don't have time to post pics or a video, but I can clearly see - and feel - that it's locking into the tab securely on the side, giving two points of stability.
I'm probably going to have to sell mine, because I've got a BG-E11 grip on the way, but I actually like the Kirk's side strap mount so much I think I'm going to go with Kirk for the larger L-bracket as well.
It's true that it takes longer to take off, but I have no interest in taking it off. It mounts more securely, and I'm willing to have the additional stability for a few more seconds with an allen wrench at home.