I believe the Adventure petrol tank crash bars do a good job and are mounted where the engine is strong.
However for the engine, you are echoing my criticisms of crash bars. I personally believe that apart from a car park tumble they are likely to write off an engine when a bare engine in the same crash would have simply needed a new rocker/head cover.
I dropped my Adventure on slimy mud at about 20 mph. The RHS engine OEM crash bar rammed into the rocker cover and could not be removed until I unbolted the cover. The Wellard Tourateck head protector was also trashed so did its job.
But had that crash bar hit any harder its likely the cylinder head would have been damaged. Additionally the head protector mounting screws (M6) came out Z shape. The M6 screws take a shear load delivered by 2mm stainless lugs that wont bend or "give". My cylinder head lugs survived but they really are not built to handle such force.
I now have Machine Art X-Heads (bought used) but even they use the same M6 lugs onto the cylinder head and the polycarbonate is very solid stuff. As it transpired mine were brittle and the lugs snapped off (vibration). I now have 2mm aluminium plates in place of the original cracked lugs. These will bend and/or the covers will crack so, while they were sub standard, I believe they are now adding protection without increasing the risk of deep damage.
I believe a good option would be shaped to fit nylon blocks butted against the rocker cover face. They could be screwed from the inside or use the cylinder head lugs but not in ways they could get overloaded in a crash. Nylon would also be easy to buff up so a simple car park tumble need not look scruffy.
Crash bobbins would look silly and potentially dig in or be ripped away, so the protector would need to be machined or moulded to fit. This shows the vulnerable area that needs protection.