I would argue it is. I see your point, once it is up past seven days you cannot delete it or edit it, so in a sense, you don't have all the control you would over something your truly owned.
What I would argue tho, is if your goal was to have your post last for life, once on the Steem blockchain, it is yours. If others steal your content, they get flagged for plagiarism, and you can pursue them legally in some places if they sell your data without your consent.
Steem gives you way more ownership over your data then Facebook does.