Presence of European football viewers does not translate to mls ratings. Even here in Portland, crossover is marginal at best. I go to the major premiership bars, and most of the guys take a passing interest in the timbers at best. Likewise, People I talk to at timbers games take a passing interest in Europe.
You mentioned part of the problem -- mls is still widely regarded as a mediocre league. There is some truth to that. The athleticism is on par with almost any league in the world, but the actual footballing talent isn't there. When you look at the successful mls clubs, the common thread is the establishment of genuine community support. Sometimes it's done outside of mls (Portland, Orlando) others, it's done once mls is there. (Seattle, Kansas city).
At the end of the day, Atlanta is just not a great sports town. I really hope blank builds something, but I'm skeptical.