Having to first write content as a post, wait for discussion to resolve, then transfer it to the wiki is a fairly major inconvenience if improving the wiki was the original goal, so we should not require people to do that.

This depends on what "improving the wiki" means. If the wiki is treated as a summary of the blog content and community canon (as it was intended, and as it is actually currently shaped), then adding content that is not on the blog doesn't serve this purpose, and doesn't constitute an improvement. Also, any good content should be posted to LW anyway.