I can certainly see that view point and felt tempted to do the same. At the end of the day though, they're still champions and usually those type of players produce their best footy at the back end. Take Fittler, Meninga, Lamb, Lockyer, Price and Webcke as example. I'm sure I'm missing a few as well, so at this stage age is just a number.
The Cowboys will struggle to replace Tamou and Hannant. Both were integral in putting the Cowboys in position and allowing them to play low risk football. Their issues could be further excacerbated if Ethan Lowe fails to recover from his spinal injury. There were rumours floating around that it could be career ending when he initially suffered the injury. While he's on track to play in Round 1, he may not be the same player he once was which will be another disruption.
Fortunately the Cows are well served by emerging backrow Coen Hess. Coen was massive in their victory against the Broncos in the semi final and has all the traits of an Origin player. He's one player worth keeping an eye on.
Not to mention, they still have Taumalolo. Jason is the best middle forward in the game and as long as he continues to grow as a player the Cowboys are always going to be in the conversation. He was a one man wrecking crew against the Broncos in that semi final and he's going to terrorise opposition teams in 2017.
Considering they still have their spine intact and still have so many key figures involved it's difficult picturing them sliding that much. I don't expect them to flog so many sides next season, but they'll be there abouts.
I'm less confident in Melbourne. At the start of 2016, there were some serious warning signs and while they were able to regroup, I don't think those issues will disappear. Koroibete, Green & Proctor are all big losses for the club and I can see a lot of turbulence as Craig tries to find suitable replacements.
Still, they're the best defensive unit in the game and have a knack of converting close games into narrow victories. I don't expect that to change and they'll find their way into the finals.
I gave my thoughts on all the teams over here:
https://broncoshq.com/threads/rate-the-competition-2017-edition.30978/
But in a nut-shell, these are the 2016 finalists I'm suss on...
Canberra - Because of the club and coach's past history.
Cronulla - Because of the pressure of being defending premiers without Ennis and Barba.
Brisbane - Because their star halfback has signed elsewhere and they have an incredibly tough start to the season.
Gold Coast - Because they were the least convincing finalists of last season.