You have to understand, that there are hundreds of thousands of horses the world over, who are sold for someone's dinner table, every year. This includes tons from the UK, Canada and the US. Doesn't matter if they are purebred or grades. The majority were not well thought out breedings, which would have been desired throughout their lives and always found willing homes. That even in our current difficult equine economy. Top quality, well bred horses are much more likely to find homes, than mixed breeds or poorly bred purebreds, bred and sold by irresponsible breeders.
This is where (I think) it will become difficult to really create a Sugarbush breed, when so many breeds are allowed in and of all types and if truly, many will be culled. I imagine it becomes even more difficult, when people in different parts of the world are all trying to recreate it. At some point, shipped semen will have to be available so the different lines can join up and be bred.
Regarding larger Gypsies in the UK. Well remember that in their background, many Shires were used in the mid 1800's when the breed really became first known and was used to pull the incredibly heavy living caravans. I know that many UK small breeders are trying to breed for smaller horses these days, but there are plenty of larger ones of the old type around if you look. Many of our most famous lines, actually go back to a Shire which came from Scotland. Not all are tobianos.