I agree with your interpretation of this.
The gospel could NOT have been preached to ALL people’s of the world — for gosh sakes HALF of the world was presumably NOT IN CONTACT with each other from BEFORE Christ was born (AT LEAST) till Leif Erickson - much less all the islands in the oceans...
To think otherwise requires a complete belief in things that the scientists/anthropologists/archaeologists who study on this subject, and BELIEVE they somehow WERE, would admit that SOMEDAY they could POSSIBLY — however remote they think the possiblity is — could be wrong.
The OP postulates that all the peoples of the Earth — ALL OF THEM were in communication in the 25 years mentioned in the OP. One cannot POSSIBLY PROVE THAT, and therefore to rely on THAT as the basis of one’s ENTIRE interpretation over such a doctrine as important to Christians as this is, IMHO, VERY DANGEROUS.
It’s a deception from hell.
It’s designed by the spiritual foisters of such nonsense into the minds of (hopefully) more or less innocent humans
to create confusion about one of the most crucial periods in all of history and Creation . . . a period when a huge percentage of Biblical prophecies warn and encourage preparation for.
Clearly God thinks this era is crucial and wants us to understand HIS TRUTH about it.
That’s another reason satan wants the opposite.