My understanding (i am not a manufacturer) is that the core / bulk / most of the frame is always going to be T700 & T800, and that key areas get fancier fiber. So, afaik, there's no such thing as a 100% T1000 frame, it would be disgusting to ride, and way too fragile (and cost too much).
In essence you are right, but's actually a bit more complicated. Especially when comparing T700/800/1000.
T1000 is stiffer and stronger than T800 which has higher stiffness and strength than T700. On the other hand, T800 is more brittle (less elastic) than both T700/T1000. In principle you could make a full T1000 carbon fiber reinforced frame, but it would cost way too much for the suppliers. So indeed, it's only used at certain key areas where weight savings can be major by changing the material and yet keeping the same stiffness.
What nowadays actually is the key factor is the (impact) strength of the frames. It would be easy to make a super stiff frame sub 600gr, but it wouldn't be strong enough. There is some need to have some 'mass' to cover the strengths.
Besides this, there is the marketing aspect. Especially with those replica frames, I wouldn't trust them on the specific type of fibers used in the frame.