Which of the following statement is not correct?

We know that they are oxyanions of chromium in the $6+$ oxidation state and are moderately strong oxidizing agents. In an aqueous solution, chromate and dichromate ions can be interconvertible.

whereas ${\mathrm{MnO}}_4^{2-}$ is not strong oxidising agent because it's highest oxidation state is $+6$.

If the oxidation state of an element increases, its electronegativity also increases. And this is why, permanganate is a strong oxidizing agent. For example, $\mathrm{Mn}$ ion has an oxidation state of $+7$ in permanganate anion which is why it is highly electronegative in nature.