drive a UJS a few winters and you understand after a few pothole freeze/thaw cycles how poorly the cheap UJS's stack up. The UJS's feel solid for awhile, but after having a couple get pounded to $h! in the winters, I don't mind carrying a few extra pounds.
One figure folks also gloss over when they dissect why a car is so heavy. WIDTH probably has more of a factor than length. It is harder to get structural stiffness to a desired level if the car is wider. The Epsilons are way too narrow yet are heavy. The CTS is a decently wide car, probably just about ok. The Zeta g8 is nice and wide, so there is that much more chassis to engineer. A car that is 70 inches wide, going to one that is 76 inches wide, the car is 6" wider, or like 8 or 9 percent wider. So I would fully expect it be a good 10% more in weight. So to me, a 3600 pound epsilon with the HF v6 going to a 4000 pound RWD much wider G8 is not a big deal. Plus, the G8 is larger than the Catera, but the Catera was not really lighter.
The g8 chassis is engineered to accept a level of engine and suspension performance the Epsilons cannot muster. It also can accept a performance level no accord can muster. The Accord can perform at an 8/10 level of the g8 chassis.....and that's fine because most folks do not exceed that performance level.
The Accord is about the only light UJS I could gain trust in as being able to withstand heavy pounding over a 5 year cycle, because only for the reason of having a trust level with Honda's engineering and products. I would not trust a Camry or Altima to withstand that.
Also, if you look at the weight specs on the Accord v6, you notice its not all that light anyways. The 4 cylinder UJS's keep their weight down pretty well, but stuff a v6 in the chassis engineered mostly for 4 cylinder application and you understand why the Altimas of the world are so light. Someone buying a Zeta is not going to accept the light duty nature of the 4 cylinder UJS platform.
The Germans are the worst offenders of weight in cars, yet no one ever likes to call them on the carpet for it. The US makes make a heavier car and get ripped for it. How can a Q7 Audi (audi, vw, mercedes, bmw...lots of pork there) can weight as much as a suburban, or a touareg weigh as much as it does for having no space inside? Let's talk about THAT for once.
BMW 135i.....3400 pounds and I bet even the tiniest spinner chick is uncomfortable in the backseat. If that's not a porky car,........
a 4000 pound g8 is positively light in comparison to something like a porky 135.