No, again, it was not meant to be a traditional comment section. It was not a discussion thread for casual readers, especially via the blog view. If you wanted a normal comment system, you could use Disqus embeds, or just use a traditional blogging software.
The reblog system was a way for Tumblr users to publicly respond to things, and allow that response to be visible to the responder's followers. The original poster would also get a notification, and they could reblog the responder's reblog to add more if they wish.
The dashboard made this slightly easier to read. Again, if you only ever experienced Tumblr on blog views and without an account, you literally never saw the core functionality that made Tumblr popular.
Also, most Tumblr posts weren't long-form text to begin with. That wasn't the point of the platform.
That explains it then. I never felt the need to make an account since I was just reading. They didn't make it clear that the service was incomplete without an account.
Well, the alternative is an aggressive full-page signup nag that intentionally breaks product functionality when logged out -- an approach used to various degrees by Facebook, Instagram, LinkedIn, Twitter, Reddit, and others. Is that really preferable?
