The parent dragons only scale to other dragons which are mountain level, the Spriggan's casual to no effort feats revolve around effecting islands which is above mountain level. at best, they are large country to small continent level. a hindrance is a threat which means that Zeref cannot fulfill his plan since END will kill him. there is no proof that Mard was wrong about Curses originating from END. just that he wasn't the creator of Tartaros. No proof Ingeel is stronger since Natsu can beat Zeref with FH. with Zeref's Immortality, Hax is the only answer, because power has no meaning to Immortals. Gray Was still in his most powerful form at the time, that does not change anything that he wasn't in best condition. and Natsu was unconscious as well yet she cannot shrink the Demon seed, so you are wrong there. and no proof that Gray was unconscious at the time of being turned to ash,
Spriggans > most dragons
@Verter don't bother, he doesn't want to admit he was wrong, since END can kill Zeref, he doesn't want to admit it