The conclusions that you drew about American circumnavigators: that we won't see them sailing Amels (or did you mean any European-made boat?) and that they sail in older boats.
As I tend to research (some say over research) just about everything, while I go about my research for an offshore boat I would want to figure out if there is a reason behind this that might influence my own choice. So, I wonder what made you reach your conclusions.
The first conclusion I think it is a fact: Most American circumnavigating tend to sail in American made boats and even if there are some really blue water boats still made by American brands, the boats are old designs, many times decades old designs, some still had a full keel or a mixed keel (not a fin keel).
I know of some Americans that sail in European boats (I am not talking about luxury boats like Oysters) but they tend to be world globe trotters or (and) very knowledgeable people. I am thinking of those two that sail for decades doing movies for cable TV (Southerly) or Cornell that had sailed an OVNI or other well known sailor, magazine and book writer that have chosen a Malo. But I think they are just a small minority.
I am not entering any discussion about the merits of old designs versus new designs, I am only stating that there are dozens of European Brands with purposely made voyage boats with new designs, for all tastes and materials, (Carbon, Epoxy, Fiberglass, Aluminum, Plywood/Epoxy), performance boats, center boarders, medium displacement boats, center cockpit, aft cockpit and deck saloons and this offer exists because there are long range sailors that are buying them and almost all are European.