The thing is, it takes a conspiracy within the Wikipedia's rank and file to bias an article significantly over a long period; otherwise normal editing and then RFCs and so forth will tend sort it out.
If it remains sufficiently inaccurate then the target will kick up a big fuss; initially within the Wikipedia, and then other places like Wikipedia Review and eventually in the press. The more people that look at the bias, the less sustainable the position of the conspiracy becomes.
Firms, organizations, or even individuals with PR budgets in the millions, or passionate, but sane, supporters can and do much better than that.
Fred