The problems started with the Lions series (countering the rush defence, as offside it is most of the time) and continued in Hansen last two years at the helm, when they come up with the concepts of "dual playmaker", "forwards playing like backs" or "let's put together our best players on the park", instead of "let's putting our best players for each position" …
ABs never really replaced Kaino (Squire was fantastic in 2016, but too injury prone and mentally fragile), they never really got it right with the midfield combo either, nor with the back 3, chowing to remain loyal to players either past their best, in the ageing curve or simply not the best in their respective positions.
Granted, saying "bye bye" to the SA teams in the Covid era was extremely detrimental to the Super Rugby NZ teams, as it ultimately created a false sense of superiority that got exposed at the international level.
My two cents anyway.
All of this is true. However, I think the biggest issue with NZ is two-fold: The rest of the world caught up. Teams 1-8 can beat anyone on their day. You couldn't say during the 2010-2017 dominance period.
France was at a low ebb. England too. Oz were good, but lacked depth. Boks were good but aging and then hit their low ebb in 16-17. Arg were worse.
Ireland was the one team that was consistently improving during the same period, culminating in the soldier field victory.
If you took peak 2010-2017 ABs, they are the best team in the world, but they aren't beating the Boks, England, France, Ireland, Argentina, and Oz 9/10 every year.
The second biggest problem is their golden generation was more platinum than golden. Even great players like Ardie and Beauden are not Richie and Dan Carter.
As you said, they've spent the last decade trying to replace Kaino. They've also never found a true replacement for Nonu or Conrad Smith.
Jordie is a great player, but he's a fullback playing 12. Goodhue was class but couldn't stay healthy. Reiko is not a center. Who knows with Proctor but he hasn't impressed me.
So you have several key positions that are still unfilled 10 years after the old guard retired.
That's where I'm the most disappointed with Razor. I thought he would tear up the Smith/Hanson/Fozzie plan and create something brand new.
Instead, he has made very few bold calls and basically stuck to business as usual.
Meanwhile you have the Boks, France, Oz, Argentina and England making wholesale changes to their personal and gameplans.