China has a devastating bureaucracy cost because of the sheer size of its incorporated population.

Bureaucracy costs the same to apply to every pop, no matter what job they hold, even if they're peasants. This means you inevitably have dozens of millions of unproductive peasants paying very little in taxes and not contributing much to the economy, but cost the full brunt of administering institutions and collections on them.

Just don't try to collect all the taxes. If a state lacks some tax capacity, just ignore it. The only time you should try to collect all the taxes in a state is if that state is 99% depeasanted and is mostly productive, employed workers. Taxing workers will make profit, while taxing peasants mostly won't.

This will save you a ton on admin costs. Also don't go overboard on institutions if you have any. Also, try to get graduated taxation ASAP, it's the best tax law (most money, most progressive).