I just drove the Mazda 787B in the first mission in the S-Class category. It allows you to shift the car with the H-pattern and clutch. Assuming it will be the same when I purchase the car, and it only comes with the one transmission option (adjustable/dog-clutch), then this is realistic, whereas the Sauber C9 isn't with sequential shifting only.
So yes, it's inconsistent, because upgrading muscle cars to an adjustable transmission and having it disable the H-Pattern is ridiculous. Once again, Kazunori and Polyphony Digital cease to amaze me with how "out of touch" they are since GT5 Prologue was released.
Here's an in-cockpit video of the Sauber C9. Looks like a full manual to me. He's operating the clutch and the stick is multi-positional (not a single spring-loaded sequential lever). I guess if I want to really enjoy the C9, I just need to go back to Forza Motosport 4 where the stick and clutch work (and REALLY well, unlike GT5's horrible clutch operation), and the sound is incredible (and doesn't sound like a vacuum cleaner as it does in GT5-6)
Watching him downshift, it reminds me of how horrible the clutch is in GT6. That's really how you should be driving for better car control. It keeps the Rev's up and avoids differential drag or lock. However in GT5-6, when you can use the clutch, it is so terrible, it often won't register most of the downshifts (if you're shifting as if it's a real car). By the time it gets it, the engine revs have dropped, and you often lock up the differential and the car spins around.
After spending more than a week in only GT6, I went back to Forza Motorsport 4 to compete in an online series race yesterday. The new tracks in GT6 are great, but Forza 4 is still soooo much better in many ways, even if it's "upsampled" from 720p resolution. I'm just not feeling any real "love affair" with GT6, as it's pretty much the same "grind" as GT5 was with several flaws and problems (with apparent new ones, such as this inconsistent transmission problem).
Maybe with all the promised updates that are coming, they actually will "fix" many of these problems... some of which carried over from GT5. Considering the six-year development of GT5, it launched with major omissions and problems, and still not everything was fixed the couple of years it was out, I'm just not too hopeful. I was a fan of Gran Turismo, but today they are falling way behind in many ways.
BTW, I completed GT5 (100%, 1,020 cars) and have reached level 319 in Forza 4 (500 cars-maxed garage), so I have quite a bit to go on to make these evaluations.