This release really does smell (stink) of that principle yes.
I mean, why isnt the performance equal to WH2 at least? I think they crammed way too many effects on those maps, with very high detail levels or at least, expensive/inefficient detal levels.
Warhammer 2 got many performance boosts down the road, I'm expecting similar here.
That said, WH2 is no performance king either, but at least it runs smooth now. CA is making a shitload of money on this trio of releases, but I think adopting a new engine for the last part would not have been beneficial to us either, I mean, that would kill a lot of cross-compatibility that the games actually do use. Mortal Empires for example in WH2. Also I think we'd have been waiting for installment 3 a LOT longer in that case.
And last... I'm not specifically happy with the way the engine works in 3 Kingdoms. But that was mostly down to the mechanics they chose to implement, man, what on earth was that anyway. And those concepts echoed on the battle maps, which was basically an open field with a bit of fog and two chunks of units on either side of it.
So maybe this 'step back' is actually a blessing in disguise. I don't recall Troy being a smash hit either.