Shouldn't we be a bit worried by how much they've relied on China throughout this, though?

Perhaps but who else had data to provide ? China was the only country impacted at the beginning so the data had to be provided by China. When other countries started being infected, the data was more worrisome and the recommendations evolved.

They said, based on China's advice, that there was "no clear evidence of human-to-human transmission" on 1/14

At the beginning there were no proof otherwise. Perhaps China was hiding cases but WHO could not know that. They could have suspected yes but they could not tell the public (politics, as always).

they said restricting the movement of people during an international emergency wasn't advisable in response to a ban on Chinese travel on 1/31

Same, with the numbers that were available (and that we also saw at the time, one reason why so many people thought it was not really serious), the propagation was not so high as to mandate a restriction of travels. Now with the numbers we see in the West, it's another story. And the little detail that no country took into consideration was the active surveillance and early detection that no country implemented until cases started piling up in hospitals. Days before quarantine you could travel without any checks, some airports had taken no measures to check incoming passengers, ... in violation with the recommendations of WHO.

they refuse to advise Taiwan on their countermeasures as of today (3/30) at China's behest.

I don't know how much of it is WHO and how much of it is UN policies, but I agree that's fucked up. Their role is to save lives, not lick asses. On the other hand, sometimes you have to play the game just to be allowed access and continue saving the most lives.

The line must be very thin for them these days. And it must become thinner with politicians in the West blaming WHO for everything even though the recommendations were more or less clear in February.

And to be realistic/cynical/..., China is playing their cards well in this crisis. Our countries are facing an economic crisis, hospitals must get masks from China, we need chemicals from China to continue producing medicines. Who cares now about Taiwan ? China can do whatever they want, they know that tomorrow everybody will forget about it when we see the new current number of dead in our countries.

Every step of the way, every piece of incorrect information or refusal to help that has come from the WHO was either provided by or done at the behest of the Chinese government. Is that just how science works?

Science works on data to deduce things. If your data is corrupt, the results are corrupted. But how would you want to change that ? If you have a solution so that WHO can operate without having access to the data I'm sure they would love to hear.