Re: see Heinberg, this is how you do a "Clark thinks Diana's lost her way" story
It's hard to tell from just these pages (and I can't be bothered to go back to the TPB to check), but it looks to me like Diana is only taller than Superman because she's standing on the bench.
I wasn't a huge fan of The New Frontier, and I'm not a fan of this particular bit (though mostly for different reasons). I don't know... this whole scene just seems like a riff on Apocalypse Now and the Viet Nam flashbacks in Watchmen to me, and it suffers by comparison to either.