I have addressed the argument that אֶחָד (“one”) refers to “compound” or “plural one”(!) in this blog, including:
To see the nonsense of this theory, I would ask a proponent of such a view to attempt to make sense of the instances of this number in the following king list in the book of Joshua:
The lands included the hill country, the western foothills, the Arabah, the mountain slopes, the wilderness and the Negev. These were the lands of the Hittites, Amorites, Canaanites, Perizzites, Hivites and Jebusites. These were the kings:
The king of Jericho one (אֶחָד) the king of Ai (near Bethel) one (אֶחָד)
The king of Jerusalem one (אֶחָד) of the king of Hebron one (אֶחָד)
The king of Jarmuth one (אֶחָד) the king of Lachish one (אֶחָד)
The king of Eglon one (אֶחָד) the king of Gezer one (אֶחָד)
The king of Hormah one (אֶחָד) the king of Arad one (אֶחָד)
The king of Libnah one (אֶחָד) the king of Adullam one (אֶחָד)
The king of Makkedah one (אֶחָד) the king of Bethel one (אֶחָד)
The king of Tappuah one (אֶחָד) the king of Hepher one (אֶחָד)
The king of Aphek one (אֶחָד) the king of Lasharon one (אֶחָד)
The king of Madone one (אֶחָד) the king of Hazor one (אֶחָד)
The king of Shimron Meron one (אֶחָד) the king of Akshaph one (אֶחָד)
The king of Taanach one (אֶחָד) the king of Megiddo one (אֶחָד)
The king of Kadesh one (אֶחָד) the king of Jokneam in Carmel one (אֶחָד)
The king of Dor (in Naphoth Dor) one (אֶחָד) the king of Goyim in Gilgal one (אֶחָד)
The king of Tirzah one (אֶחָד) thirty-one kings in all. (Josh 12:8-24 NIV)