I am saying that the core gameplay was conceived by the developers, and only afterwards did the situation arise that the developers and management couldn't agree on a solution. During the initial phase of game development, management lays out a direction, but it's up to the developers to create the basic gameplay. Like, management says that they want to have a giant hammer as the main weapon in the game, but the developers get to work and come up with a combat system. Said combat is the reason why this game was never any fun at any point, so that is the developers' fault.
I didn't put all the blame on the developers. I said the game should have been canned instead of continuing development. This includes especially the management decision to change the artstyle, because poor core gameplay is going to remain poor core gameplay regardless of the game's looks.
I'll ignore the first two sentences of your last paragraph because they don't apply to me. Like I said in my previous post, the aftermath is that development at NST has run smoothly since then. So the question remains, what's there to learn from this? The culprits of the failed Project H.A.M.M.E.R. are gone; the developers have resigned, the management has been replaced or if it's still in place, it hasn't committed the same mistake since then. Additionally, how many Nintendo-affiliated studios have gone through something similar since 2009 when NST's failure got cancelled for good? It doesn't seem like there have been any significant problems, so it looks like you are trying to make a mountain out of a molehill.
First, I've hardly made a moutain out of anything.
Second, again, I'd like to know why you believe the development team was unsupervised while they worked on this project. Most of NST's games have had Japanese transplants in the producer role and I believe that was the case here. Usually project management has more than a bit of say in the direction of a game right from the very start. I can think of absolutely no reason why it would be any different here. The game did not get to the 75% complete point before the people in charge of the project peeked into the room.
Management is ALWAYS responsible for a project from start to finish. If, as you say, they were not paying attention to what was going on until the last minute, then that's a much worse allegation.
As for the studio not making the same mistake again, that's true. They've worked on nothing ambitious since then and what they have worked on has been Japanese style games.
That, actually, leads me to believe that Nintendo has learned something from the NST situation: if your intention is to make a "western style" game, giving project control to transplanted Japanese management doesn't make much sense.