One problem for Sanders is that he has little support outside the Latte Liberal left wing activist crowd. Obama was able to fuse together the activist base and added on African American support to win the primary. It was a close run thing, he even lost the popular vote.
Blacks and other minorities appear to be sticking with Hillary. Sanders will struggle to break out of the activist base. Atlas and Daily Kos are not even remotely close to the average Democrat.
Depends what tabulation of the popular vote you're looking at.
I agree with what you've said here for the most part though.