Don't forget that it's baked in on the labor side as well. NUMMI was not a 'fix' of a GM plant. It was a new venture started where a previous GM plant had closed.
Back to my original point, GM couldn't adopt the changes everywhere despite what they "learned" without firing everyone at the existing plants to start with a clean slate like they did with NUMMI. Once the relationships are poisoned, both sides need severe restructuring (i.e. leadership changes) to fix it.
I disagree with you that this (or anything) proves "both sides need severe restructuring". It's not like GM's managerial apparatus had a spiritual breakthrough, made deep internal changes, and then worked hard to change the worker-labor hostility that they had spent decades building up. I do agree that starting with a closed plant and bringing back workers made this easier for Toyota to sort things out, but there's no reason to think it would have been an impossible task if they'd started before the plant closed.
As the TAL piece explains, GM never really tried. They ultimately preferred their poisoned relationships and lower effectiveness, just like they had for the decades that Toyota kicked their asses. Toyota's higher per-worker productivity and greater quality goes back to at least the 1960s (per Rother's Toyota Kata), and this became a keen problem for the big 3 starting in the 1970s. GM's managerialist culture means that the managers had all the power to fix this. They never have, even though they were on the road to bankruptcy.
You can't take a system like managerialism, or any system whose purpose is the creation of a power imbalance, and then blame "both sides" its failures. With power comes responsibility.
10 years later, I totaled it and despite being a lot better off financially than I was at 16, I decided to buy another one. It's just such a solid car, maintenance is easy on it, etc. It's sad to me that there aren't more of the solid, low-tech, low-cost cars that NUMMI was so great at churning out.
Maybe one day Tesla can get electric cars to that type of economy of scale, but I think it's going to be a while.
The heartbreaking part is that even when GM saw it happen, they couldn't really get it. Manager-labor hostility was too baked in on the management side for them to really change.