First, let me say this is just my opinion, and secondly, that I like the Armada and would love to see more on the trail (and my sample size with one is small and from an older like 05ish model year).
I run an older GX470 and my brother had an older Armada. The Armada is a very comfortable and from what I have seen dependable vehicle (interior is not the same quality as an LC). It is heavier and larger (longer and wider) while on paper it might only be a few inches, on the trail it seemed like feet. On the beach or in the desert no problem, but here in the southeast, it was a minor inconvenience several times.
But for Overlanding, from my point of view, the Armada has 2 real problems, that most likely can be solved with money:
#1 You will need lockers in the rear at-least (for the type of trails I like):
As the traction control for offroad was not nearly what the same era Toyota/Lexus had or much less what the newer Toys, LRs, and Jeeps have.
#2 if possible re-gear 4 low (for the type of trails I like):
He would put it in 4Low and go down a steep hill and have to hit the break constantly (making him slide) or gain too much speed. I would go down the same hill in 4Lo and be bored because it was too slow. The 4low was not low enough for use in steep mountain terrain and weight of the Armada.
To the dependability, it now is owned by a good friend of ours and has almost 300K miles on it. Still running as a daily driver with only routine maintenance (other than replacing the headers with aftermarket as stock tended to crack).
The Motor in that thing is a beast btw. After the upgraded headers, it would beat a Raptor from stoplight to stoplight.
If you get at on the trail I would love to tag along as I am in WNC, just about an hour and a half from you. Gorges and Horsepature Rd are right there for us.