The following are just my opinions and are not backed by any scientific measurements or detailed studio photographs under controlled conditions, so take them with as many grains of salt as you wish.
I’m confused with comments like “suboptimal processing by Adobe” of Z9, etc. The Adobe RAW processing can be set as a preset to any values you prefer. So far I’ve taken about 10,000 images with my Z9 using HE* and I’m happy with my Adobe LR Classic, Photoshop workflow (occasionally also using Topaz DeNoise and NIC/Silver Effects Pro).
I do not rely on Adobe’s default settings for color profiles, sharpening, etc, for my Z9 or any other camera that I’ve owned (Z7ii, D850, etc). Instead, I create a custom sunlight color profile for each camera using a ColorChecker Passport and software from X-Rite/Calibrite. I then create a LR Classic preset for each camera type (Z9, Z7ii, D850, etc) with the develop settings that I prefer to start from, including the amount of sharpening and the Custom sunlight color profile that I made via X-Rite. The LR Classic camera preset (specific to each camera type - Z9, Z7, etc) is then what I use during the LR import process.
Just to me, I can tell no difference between Z9 HE* and compressed NEF, and both of those seem very close to Z7 and D850 NEF files with respect to image quality.