Far be it from me to be contrary, but...

Gotta defend a fellow lefty with a righty gun!

1} "is the strength of the action largely borne by the bolt itself?" Not sure exactly what you are asking here but if you are referring to the containment of pressures, yes. This sytem is a barrel-extension system as for principles no different than that of a Remington 870. Bolt lugs bear the strain inside the removable receiver ring.

2} "Why not just detach the whole action from the stock, ala Mannlicher, or unscrew the guard screws." I think in order to maintain bedding of the rear action portion. I do not know by what method the barrel is attached, but if it is stiffly done, it seems to possess no inherent accuracy problems. That is, action resists recoil and provides for security for the barrel extension, barrel extension contains pressure and probably the barrel is freefloated? I don't see a problem as long as the barrel extension locks up tight. Does that rail possess a cam lock of some sort?

3} "the mount is clearly too weak to stand up under the recoil of the rifle combined with the weight of the scope." I don't know. Very light shotguns are used with various cantelever mounts and hold up fine. I tested quite a few over hundreds of heavy slug loads years ago and found very good maintenance of zero. Dropping this gun or bumping it might be another issue, but mere strength under recoil shouldn't be bad in my opinion.

BTW: Looks like the animals were shot with a different rifle. Maybe this thing won't shoot!

As for taste, it is certainly extreme, but beauty is in the eye of the beholder I guess. I like a more delicate Schnabel, but otherwise, I kinda like it.

But then, I love the roccoco Einsiedeln Chapel of the Black Madonna, too.