The defense really should be primarily built through the draft, and Benning has a decent stable of Hughes, Juolevi, Woo, Rathbone, and Tryamkin (hopefully) to show for it. If Benning has the opportunity to trade for a solid foundational piece, he should. The FA period always seems to be where average players values are drastically inflated with this year seemingly no different.
Fixing something quickly doesn't usually mean it's been adequate.