By most standards, China absolutely is a great power.
Their problem is, they live in the era of the most powerful nation ever to exist; you used to sometimes hear about how the US had gone from 'superpower' to 'hyperpower.'
As Cherico posted above, they also have a much more fragile economy than most think, and a lot of the economic strength they do have, has been based on other countries letting them get away with shit for decades, that Trump has been starting to shut down.
Like any centrally planned economy, the more controlled and planned it is, the weaker it is, and that's catching up with them.
Once their economic cascade failure hits, it's going to be questionable whether they'll count as a great power or not anymore. If we (and they) are lucky, it'll be the end of the CCP. Even an incompetent strongman dictator would be better than what's happening now.
If post-collapse they have a new form of government and leadership, they might become an enduring great power, rather than a nation that gets great power status by sheer dint of population. A population advantage which they have been deliberately wasting, and which is steadily catching up with them.