Types 7 and 9 are actually super different from one another. While they both suffer from a deficiency of inwardness, the causes and reactions are quite different.

If you think of a 5 as being uncomfortable with the outside world, then think of a 7 as being uncomfortable with their inner world. 5s deal with that anxiety by withdrawing into themselves (like a brain in a jar), and 7s deal with that anxiety by constantly externalizing themselves (like a bouncy ball). 7s also have an ego structure that revolves around planning... "Oh, I know!!! First I'll do this, and then I'll do that!" There is an enthusiasm for possibility and experience.

9s have a psychological inertia. The best way to think about this is to consider what the Enneagram actually is: A system which defines what one perceives to be missing from the whole version of oneself. In other words, we all think that there is something we need in order to be what we think we should be.

For example, 3s seek success through appearances, 4s seek happiness through pain, 5s seek wholeness through isolation. Every type has a definable fixation... except type 9. So, 9s sense of wholeness isn't defined as lacking anything in particular, so there is an internal indolence because there is nothing to chase. While the "loss in being" is palpable for all the other types, for 9, it is actually a lack of specific craving/loss. Externally, this can give an appearance of spiritual fulfillment or earthy fullness , but it is a false spiritual fullness because it hasn't identified anything to be missing and instead just says "I am".