Yeah, look at the preferences window. Aperture is using something called "ProKit" which is a bunch of UI elements that were used in Final Cut Pro (prior to version X), etc. And it's pretty obvious when launching Aperture on Sierra these days that it's lost in time.
Well, I don’t see anything “clipped” about that, and I don’t know what that has to do with raw processing.
That's not how it works. The raw processor in the OS changes, but Aperture is "locked" to a specific version.
Yes, that’s exactly how it works. Go look in /System/Library/CoreServices. See that folder called RawCamera.bundle? Every Apple provided app that opens raw images uses that; Preview, Photos, iPhoto, and Aperture. It’s also available to be used by third party developers, so for instance, Acorn, Pixelmator, and Affinity Photo all use it for raw conversion, though Affinity also offers the option of using their own processor. You can open the RawCamera.bundle and look at the version.plist file, and then look at About Aperture, and you’ll see that they’re both the same version. If Aperture were somehow locked to an older version, then there would have to be an older RawCamera.bundle in CoreServices, and Aperture would have to be lying about what version it’s using in the About window.
This is how software works; Aperture is not calling new APIs and it's not getting enhancements made to shadow/highlight detail, etc. Otherwise when you upgrade the OS, all your pictures would change how they look.
As Bob has already pointed out, you can open older files and see the warning about being processed by and older version of the raw processor, and if you reprocess, they do change.
I've tried this with photos from my Leica M9: I had some poor raw conversions on skies with Aperture, and in the past 2 years, those photos render beautifully in Photos.
Which suggests that the default processing settings for Photos and Aperture are different, which is what I would expect from consumer vs. professional focussed apps.
No. All my cameras are fully supported by Aperture.
Where did I say anything about your cameras being unsupported?