I think the CA18DET gets the bad rep because there's other Nissan engines out there that make more power, more torque, and have better aftermarket support.
The CA18DET is a good engine, but why spend money on a "mini-rb" when you could get a RB20DET for almost around the same price. It's not the big grand daddy of the RB Family, but it's a Inline-6 2.0L vs a 4 Cylinder 1.8L. As you said, there's no replacement for displacement.
I've had a RB20DET in my last 240SX. I've drifted and abused it(it loves to rev to high rpms), but I also daily drove it. It was very reliable, got good gas milage when I wasn't driving like a maniac, and the sound it makes is just music, hahaha.
I've also had a SR20DET in my first 240sx. It's just that the demand for the SR20DET makes the engine more expensive. As another member already said, it's a lighter engine because it's an alumminum block and it puts out more HP and torque with tons of aftermarket support than the CA18DET.
With all that said, the CA18DET is just given the bad rep because no one really look to it as they do a SR20DET. Also, because a couple of SR20's in those civics will be good for race wars (some sh!t like that, hahaha).