And they used an example there to elucidate what they are talking about using the term for "Great Politicians" to prove their point.
WSM & WSC being the Strongest in their respective areas while also being the Greatest Pirates does not imply in any way that all the Greatest Pirates are also "the Strongest".
The term "Yonko" being a term of influence & not a measure of strength has been proven using two examples in the manga already - Teach & Buggy.
Teach only became a Yonko after beating Marco & conquering territories, meaning strength alone is not enough.
Buggy became a Yonko because he had two powerful men, one of whom is worth more than Buggy himself, under him.
Individual strength of course helps, but without a crew and territories, even if one was the strongest of all time in OP one wouldn't be an Emperor. And that is what the translator said as well.