Nearco was very much a son of Phalaris; hence the potential for a huge rear end. Phalaris was a danged funny looking horse.
Sprinters are actually quite decent for sport horses, as long as they have Nasrullah/Mumtaz Mahal type conformation. Milers seem to have created the best/longest lasting sport horse lines. IMO, most of the lines that are really, really good for sport jumping are the speedsters with the Mumtaz Mahal type conformation because they have so many fast twitch muscle cells. It gets a bit dicer for eventers, because stamina is still of important–very few other horses are asked to gallop at 570 meters per minute and jump for 10-11 minutes, which, until two years ago, was 11-13 minutes with 45 jumping efforts.