No, not every conjecture has been researched. But if you're at all familiar with editorial policy on wikipedia, you'll know that only mainstream sources are typically treated as WP:reliablesource (e.g. wapo, huffpo, cnn, nbc, occasionally salon and vox tier) and the vast majority of right leaning sources (aside from fox) are effectively blacklisted. Not to mention the regular editorial bullying on politically sensitive pages that reinforces the bias by chasing away neutral or non-progressive leaning editors with alternative points of view.

Also if the allegation is that wikipedia has an editorial bias, I wouldn't necessarily trust wikipedia's own evaluation of it's bias.