Both sides try to manipulate it, but in certain topic areas, the numbers are highly skewed such that one side wins almost all disputes.
For example, Wikipedia's definition of Zionism was updated to include "as much land, as many Jews, and as few Palestinian Arabs as possible". There are absolutely no other dictionaries or encyclopedias with definitions resembling that; Wikipedia is uniquely biased there.
When you can't eliminate bias completely, as I think it is the case here, the next best thing is transparency, and you can hardly get better than that! Maybe no other dictionaries or encyclopedias describe it like that, but no other dictionaries or encyclopedias give so much detail on why it is described the way they do.
In the end "Zionism" is just a word, the meaning of it is what people make it to be, not what dictionaries or encyclopedias say it is, and considering the current situation, it means different things if you ask different people, so bias is unavoidable. Of course, if it is etymology you are after, the Wikipedia article covers that too, with plenty of citations.
I think you would have a point if such biased statements had tags such as [1], directing readers to the relevant discussions. Attempts to add such tags are normally reverted by the usual anti-Israeli editors.
So we have theoretical transparency, but no hint to the reader that they may want to look into a dispute rather than accepting the content at face value. Readers could peruse the talk page, but it contains several hundred (mostly archived) discussions.
The main page history also contains thousands of smaller disputes, where communication was done via edit summaries. Realistically, readers aren't going to dig through talk page archives, let alone years of edit history.
For example, Wikipedia's definition of Zionism was updated to include "as much land, as many Jews, and as few Palestinian Arabs as possible". There are absolutely no other dictionaries or encyclopedias with definitions resembling that; Wikipedia is uniquely biased there.