Just a couple of general observations on the mainsheet to boom attachment on Super Maramus. I do not think this part is underdesigned. I think the issue is that boats are sometimes sailed in ways that the designer did not anticipate or allow for.
We had Harmonie for over two years before I first heard about this issue on another SM. I saw the damage, and pretty quickly afterwards heard of another boat with the same issue. I realized I hadn't looked at this part closely on our boat, so put that on the checklist. A detailed inspection showed that it looked exactly as it did when it left the factory. This after 22 years sailing on two circumnavigations, and accumulating well over 100,000 sea miles. Based on what I saw, there was no reason to replace or change anything. So the idea that the design was faulty or fragile didn't seem to make sense.
It took me a week of thinking why this disparity might be before the light bulb lite up and the connection was made. A rigger with a lot of Amel experience confirmed the answer: Accidental gybes. They can put a HUGE load on all the parts of the rig, especially the mainsheet attachment. Everybody has them, (hopefully rarely!) but with the way the SM is set up we can really reduce, or completely eliminate, damage done if we sail the boat "right".
The key to reducing the shock load on the boom is to ALWAYS, ALWAYS, ALWAYS move the traveler to the side of the boat where the boom is eased out. That minimizes the length of the sheet, and hence the swing of the boom and the peak velocity of the boom during a gybe. NEVER sail the boat with the boom eased far out over the rail using only the sheet while keeping the traveler centered. It is very inefficient in terms of sail shape, but much more importantly it is potentially risking damage to many parts of the rig if things go wrong.
I am convinced you can beef up this part all you want, but it you have a full flying gybe, stuff can still break. I have seen booms snapped in half, and rigs taken down by accidental gybes. The forces can be darn close to irresistible, so everything that can be done to reduce those forces, should be done, and done every time we turn downwind.