OP, I think you misspelled the sire's dam's name on allbreed. If it's Starry Serenade instead of "Screnade", that is
. She is on there and would bring some more interesting lines.
With the Polish Arabians in there, you can't go wrong with any sport. Poland breeds only proven performers to proven performers. Mostly racing. And the "Bey" lines are also performance bred (had to say that, sorry
As for stocky or dainty.....anybody who knows Arabians will know that their bones are denser than any other breed's and smaller horses carry more weight in relation to size than larger horses.
IMO, if that foal grows up well, with lots of room to run, with a herd, and is fed properly, I don't see where there should be a problem doing endurance. Maybe not the Tevis, but not very many at all make it that far, regardless of bloodlines.