Yes, the in-5 is a horrible
Yes, the in-5 is a horrible engine compared to what can be done with today's tech. I disagree on the Cruze Eco for one reason, though: I have yet to drive an "Eco" model that actually gets the mileage they claim it gets. Haven't driven the Cruze Eco, but I suspect it will be like all the others: hype with no payoff. The diesel, however, I have driven and unlike the Eco (if that engine does pay off in efficiency), it was actually fun to drive. Tons of get-up thanks to that low torque curve.
The Mazda6 will be an excellent comparison, you're right. That's comparing a high-compression gasoline to high-compression diesel on what is otherwise exactly the same platform. I drove the i-ELOOP 2.5L gas version for a week and it was phenomenal and makes it easy to get 40 mpg on the highway and I believe they've said they're only expecting a couple/three more MPG for the diesel.