I've certainly enjoyed driving Armadas more than full-size GM and Ford SUV's I've had as rentals, and would pick an Armada over a domestic SUV. The Armada is made in Japan and it shows, and the driving dynamics are not bad considering the size. But, to your point, while it's better than Tahoe/Expedition build quality, it's not Tahara build quality either. A better comparison to the Armada would be the 2nd gen Sequoia, which also has the large V8 and IRS.As well as no way being as reliable as the hundy....the above is big reasons why I would never own an Armada or any Nissan. Although it is splitting hairs....I think the 80 series is the perfect size for my liking but everything else about a hundy puts that hair back together.
LX570s have come down quite a bit in price - $30-50K will get you a nice one - so that's what I'd get if I needed a larger SUV.