The thing is, "Tsaesci" only exists in text, because it's too hard for the voice actors to say. That's why everyone calls them "Akaviri" instead.
That's a pretty wild claim considering all the stuff they have people like Chris Plummer and Max von Sydow saying in Skyrim. If the celebrity voice actors can manage, I'm sure Beth can hire a few professional VO artists to say Tsaesci.
I never said the invasion didn't involve the Tsaesci, just that this pretty clearly shows there were humans too. Obviously Pale Pass in Oblivion cleared this up several times over (letter, ghosts), but the 'humans-were-eaten' folk just can't let it go, even when the Tsaesci are already shown to use the word 'eat' metaphorically.
What Esbern says, by the way, is that some of the wall-carvings in the entrance show the Akaviri craftsmen (and while it's hardly a smoking gun, he does in fact use the word craftsmen) adapting the "more fluid Nordic style." It's a pretty big leap from that to "oh and also they started depicting themselves as humans, for some reason."
And yes, I think this means the Rimmen are the descendants of the Akaviri Humans/Dragonguard.