It's tough to know if and when to blow up a team. Teams like Geelong and Sydney have managed to re-stump while being competitive. As others have said, 2015 wasn't convincing, but we did finish top of the ladder, so I'm not sure you start a rebuild then.
2016 it was obvious we were off the pace. But there's only so much you can do in one off-season. We de-listed over 10 players last year, including some fine servants. Less than a fortnight ago people on this site were complaining that we had blundered by not keeping a 29 year old who couldn't run or kick. I'm pretty sure we've got that type of player covered at the moment. Winning the ball isn't a problem. Using it is. Barlow, de Boer and Mzungu don't help us in that regard, even though they are still handy players. We were moving in the right direction.
We brought in younger players. Hamling has not been great, but he shows good signs. Hill has been good, and should be with us for years. McCarthy will be alright. If A Pearce and Apeness are ever fit, I reckon they'll be players.
It takes time. Harvey took over in 2007. It took until 2010 to put together a winning side. You could say Lyon knew he was rebuilding mid-last year, so by that count he still has a few years. He wouldn't be my choice to rebuild a team, but two weeks in seems a bit early to declare Lyon;s rebuild a failure.