Sure, it will be easier for the powers that be to take down something you posted on Tumblr than to take down a Tor hidden service. But that's a completely different matter from publishing anonymously in the first place.
The author also seems to think that publishing images and videos anonymously is harder than publishing ASCII text anonymously. This may be right, but not because of the reasons he cites. If you already have a medium where you can publish ASCII text anonymously, nothing stops you from publishing your media in a base64-encoded form. The real problem with publishing images and videos anonymously is that those media files often contain lots of entropy that could help identify the author, such as location information. No amount of Tor trickery will keep you anonymous unless you thoroughly scrub your media files.