Here is what the Sea Kings said about Luffy and Roger being able to hear them :
In other words you are not remembering the story well
The sea kings never said only Roger could hear them, they said that someone hearing them happened once before.
Secondly :
Roger had indeed no way to decipher the poneglyph..
BY HIMSELF. He could only hear them. The fact that oden was able to write - and therefore Roger wasable to understand and write something - was prepared ALL THE WAY BACK in Skypiea here:
When we look at the interview and the structure of the story, we can say that Oda's purpose was to make Wano the center of his story at the beginning (hence why it thought it would last 5 years). So in reality, there are reasons to think that Oda had already Oden in mind WAY BEFORE he wrote skypiea.
There was no retcon here.
Roger
had to be helped by someone to write the poneglyph, EVEN when he was able to "hear" the voice of the stone.
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In other word, the "critik" here stands on nothing but missunderstanding and missremembering of the story.
That's, once again, a good thing and not a bad thing.