Manly also had a fair bit go against them injury wise outside of Turbo. Their spine was a mess for most of the year especially.
Through that though DCE was still their best or close to their best nearly every week. The Cowboys had plenty of dire seasons under JT as well, but through even those years he was still constantly working hard and busting his ass to compete and drag his side back up the ladder. That is the difference between those guys and Milford.
You're also forgetting that a portion of DCE's contract value is made up in the things he brings to the club outside of his own on field ability. Leadership, professionalism, experience and driving standards on and off the field, and that's before you add in the commercial value he has to the club and it's image which is hard to put a price on but he's highly marketable. Milford doesn't bring any of those attributes to the Broncos currently.