No American Gadol is on the level of Rav Elyashiv, Rav CChaim Kanievsky, Rav Shmuel Aurbach or Rav Aharon Leib, so it’s irrelevant what Americans hold. The Novominsker Rebbe publicly said that we should shudder at arguing with Rav Chaim. I challenge you to please find me one Rav who paskins issue vheter who wrote that a boy who is yitzro misgaber alav or has no fear of insufficient food is allowed to delay, who says that Chazal and the Shulchan Aruch were mistaken when they held that once it’s yitzro misgaber alav you may not delay.
The word Aguna for a girl who is having trouble finding a shidduch is found in Kidushin Daf 41 in Tosafos and Midrash Rabbah Achrei Mos. Agav, the Midrash says that Nadav and Avihu died for making Agunos.