Their problem is not that their data is bad. Their problem is that they are acting like a political entity when they are supposed to be an impartial, data driven, scientific organization. For example, the WHO railed against common sense risk mitigation strategies such as travel restrictions (i.e. isolate China) early on with COVID when they were precisely what was needed to reduce risk. They did so for political or monetary reasons (closing borders harms economies). Xi latched on to this and used it as justification to keep borders open. Unsurprisingly, COVID subsequently spread rapidly between China and countries that had maintained open borders with China.
It is not the WHO's job to consider the economic ramifications of their policy suggestions: that is the job of politicians. It is their job to put forward suggestions for how to limit the spread of disease regardless of the impact to economies or governments.