I've never sat in an LC's 3rd row actually, but my uncle had an LX 570 and the 3rd row wasn't a good experience at all for me (I'm 6'1"). Most of the time we'd just stuff my nephews and nieces (his grandkids) in there because the adults never wanted to take those seats.
Another uncle drives a similar model-year Sequoia and they very often seat adults in the back, so Toyota definitely has the platform to build a comfortable 7-seater in TNGA-F.