GM has been doing a good job improving the cars--granted, they started from a low point and had clear guidance from ALCON on where improvement was needed. Now that GM is near-parity with the competition and no longer has obvious deficiencies to clean up, we'll see if they understand first principles or were merely copying their betters.
The interior, which has always been GM's low point, has improved markedly between all four generations. The chassis has always been good, but the suspension has improved by leaps and bounds. I can't speak to the seats in the 4th gen, but the improvements between gen 1-2 & 2-3 were huge. For powertrain, the differential now seems to be bulletproof, even under modified power levels.
The brakes have remained consistently mediocre. There's barely any difference between the OEM Brembos after normalizing for vehicle weight. The Brembo pistons are still aluminum (which contributes to the squishy pedal and transfers heat into the fluid) instead of stainless or titanium, and they're still using the squishy Ferodo HP1000 pad material for low temperature performance. Stainless pistons and Ferodo DS2500 pads should be standard.
The manual transmission is still using a remote linkage instead of using the extended T-56/TR-6060 tailhousing. As a result, the shifter is sloppy when new and the driveshaft is longer than it needs to be. The long driveshaft lowers the critical speed and mandates a steel two-piece driveshaft at the price target GM wants to hit. I can't see GM ever replacing the two-piece driveshaft with a CF single piece driveshaft, but the remote linkage can and should be eliminated.
Audio is still abysmal. You don't see paper cones these days outside of GM, the mounts are plastic (at least they're giving us a little strip of foam now so it's no longer plastic on metal), the rear deck mount is unisolated plastic and rattles from the factory, and the amplifier is so underpowered the bass has to be delayed in software to avoid overload, causing bass hits to be time-shifted out of phase with the music. The cheapest garbage you can buy on Amazon is a quantum leap over GM OEM.
I could probably do a whole post on the subject of rubber and nylon bushings; if you're designing for low cost and short lifetime they're hard-to-beat materials. Rubber does a great job transforming vibrational energy into heat and the manufacturing costs are very low to make a rubber bushing. Likewise, nylon has self-lubricating properties and the costs are low.
I really don't have any problem with GM using nylon bushings, but I do have a problem with their assumptions for how hard users load those bushings when they shift and brake. You can't just replace a bronze bushing with a nylon part and call it done; you have to make the assembly large enough to distribute the load and prevent plastic deformation.
For rubber bushings, you're in a battle against time. Just like car tires aren't sold past 4 years and have a 6 year lifetime, rubber bushings oxidize and dry-rot in 6-10 years, which is conveniently outside the warranty period. Just because the point at which the bushing has cracked and is falling apart is outside the warranty period doesn't mean the bushing hasn't functionally degraded within the first few years of service. I started noticing the shifter linkage bushings in my ATS-V being unacceptably bad at 15k miles, as an example.
I don't know a single GM owner that's using the car for its intended purpose that hasn't replaced every bushing within 5 years. GM probably doesn't recognize the true impact of their design decision here, because the majority of bushing replacements are done by the owner (owners could have GM do replacement under warranty, but replacing a garbage part with the same garbage part is pointless and frustrating).
We're at the point where 60-80A polyurethane bushings should be standard; the cost delta is less than a hundred dollars, and you get all kinds of benefits in terms of reliability and brand quality perception in addition to technical benefits (e.g. linear instead of progressive control arm motion). The Precision Package revealed to me that GM is not ignoring polyurethane, they're just ignorant. A set of soft polyurethane bushings on the rear subframe and control arms would've done wonders for handling and cost about ten bucks instead of the $1k+ billet aluminum arms GM offered instead.
This post is already too long and I don't want to go into greater depth, but there's a lot of things you can do with polyurethane that you can't easily do with rubber (e.g. machining, casting, or 3D printing polyurethane structures that have different stiffnesses in different axes) that makes it a superior option in addition to the fact that it essentially never wears or ages out.
I definitely understand a lot of your post and I agree with a lot of it.
The main things you have to keep in mind are scale, cost per unit, and quantity of parts. They have to consider cost per part based on a very large number. You referenced the different material for the bushings. Something that is less than $100, usually means over $90. When you think about that multiplied by something as low as 50,000, you are talking about $4.5 million. Now, imagine that difference for just 10, 20, or 30 parts. When the cars get excellent reviews by customers and auto magazines, etc. It makes it hard to warrant a change.
When you build cars on a conveyor belt and you finish one every 5 minutes, you have to think about variety of parts being installed on the line. The more complicated it is to do different parts on each car on the same line, the slower it is, with a higher chance to make a mistake. The CT5-V Blackwing and CT5-V are still a CT5 at the end of the day and built at the same plant. You cannot upgrade every component just for the CT5-V and the CT5-V Blackwing. They don't build 50 CT5-V Blackwings in a row, then 100 CT5s in a row. It is completely random. Imagine what it would be like to ask 50+ people (probably more with 1,400 employees) on the line to look up every VIN to verify which components it gets. I have been to the GM plant in Arlington and I can tell you first hand, this would not work.
I assume you are not talking about the AKG system when you say the audio is abysmal.
One example:
I have driven the CTS-V and the M5 at the Circuit of the Americas in Austin. The BMW M5 had significantly more "brake fade" after multiple laps compared to the CTS-V. They could make Carbon Ceramic brakes standard, but if they can match or beat the competition with the current compounds, why would they? Granted, I have not driven a 2025/2026 CT5-V Blackwing and M5.
2025 M5 60mph-0mph = 115-118 feet
2025 CT5-V Blackwing (No Precision Package) 60mph-0mph = 100-104 feet
Yes, the materials you are talking about are better than what is currently used. But, every vehicle in it's class will have components and materials that could be upgraded. Profit & loss, customer base, competition, MSRP comparison, performance, etc. are just some of the factors that go into desiging these vehicles. These vehicles are undoubtedly amazing and above their competitors.
I 100% understand your point. I just want to put it in perspective from the manufacturers point of view.