The Flex is close to identical in form factor and size to a pre-oil crisis station wagon. Probably has less ground clearance too. It takes the honesty of a professional political to call it an SUV.
Are you comparing to the car market of 50 years past to justify a vehicle that is more akin to a tank than a modern regular car?
Like you say, the term itself is meaningless but it does encompass the current class of vehicles that are needlessly big, heavy, and so high of the ground that some tanks literally have better forward vision than those SUVs.
I don't really care what Americans drove 50 years ago, I care that most cars sold here (EU) are way oversized for practically no reason that the consumer cares about.
I'm comparing to pre-oil crisis land yachts because I don't want a bunch of nit picking jerks to complain that it's wider than the 1990ish county squire or caprice wagon I would have preferred to to compare it to on account of the comparable internal dimensions.