Yes what is stated in the Watchtower is interpretation. We need context.
I guess what persuades me that the "wisdom" of Proverbs 8 is not a mere quality is the statement in verse 22, "Jehovah himself produced me as the beginning of his way, the earliest of his acheivements from long ago".
If wisdom, the quality, were "produced" at a certain stage, it would imply that at some point Jehovah didn't have the quality of wisdom, that he had to create it.
It seems more straightforward to believe that he created an individual who would be a container of his wisdom.
Gopher