Honestly, this is an awesome idea that I'll have to try out sometime.  Can't believe I never thought of it.

LOL, is this some kind of revelation?

To me it is  I never really thought about putting a head on a QD plate.  It makes sense, but I never really put 2 + 2 together on it.

Did ARMS #22 throw levers by Dick Swan wrong you at some point in your life?

Not really, but I can see the point if you’re traveling and need a ball and gimbal head, but are on very limited space.

It was against bringing a separate tripod (I think) I do agree on the failure point though. Just thought it was interesting.

It's difficult to unscrew the ball head, if it's held on with Loctite.

It's a matter of convenience.  The same reason we put quick release clamps on a ball head so we can mount the camera/lenses quickly.  Those would be more secure when screwed on, too. If you are a pro, and time is money, then the convenience might be worth the (very small, IMO) risk of failure.

Really, the biggest weak point I see, is that there is one more quick release clamp in the setup, which could be accidentally opened.  I have a Gitzo tripod, with RRS ballhead and clamps, and I can't see any of that equipment failing under normal use.  It's high quality stuff, and you would have to beat the shit out of it to get something to physically break. Sure, it might break if you dropped off of a cliff or something, but then the camera/lens would be toast anyway.

Well anyway, it's a non-issue for me, because I only have one ball head, and no gimbal.