Since both are grammatically possible, perhaps it would be better to understand it as a double entendre. In other words Jesus wanted to convey both ideas. It is not a case of either\or but both\and. Just my two cents on the matter.
Gen. 1:1 "In the beginning God created the heavens and the earth."
These are not recorded as two separate events but one. God did not create the heavens then the Earth.
Yet it states the text that "sons of God" sang\shouted with joy when He did so (i.e. when he laid the foundation of the earth).
"when the morning stars sang together
and all the sons of God shouted for joy?"
Thus the "sons" of God" must have existed before that event.
If you do not think these "sons of God" are angels that is irrelevant to my point in regard to your claim.
You stated:
Whoever they are they existed before the Earth. God's point is Job was not there when God "laid the foundation of the earth" and the sons of God sang\shouted with joy when He...
Job 38:4-7 seems to suggest other wise.
4 “Where were you when I laid the foundation of the earth?
Tell me, if you have understanding.
5 Who determined its measurements—surely you know!
Or who stretched the line upon it?
6 On what were its bases sunk,
or who laid its cornerstone,
7...