Lesser known heroes?
You do realise that Captain America, Thor and Hulk were also lesser known heroes right? And no one knew who the Guardians of the Galaxy, Doctor Strange or Ant-Man was. When I say "no one", I mean the general populous of course. Have a look at the box office numbers for the phase 1 films for Hulk, Cap and Thor, they are extremely low compared to what they make now. Iron Man was some crazy lightning in a bottle scenario because I'm pretty sure that in 2008 barely anyone knew who he was.
What I am trying to say is that it doesn't matter if Marvel has lesser know characters in phase 4 because they had lesser known characters in phase 1 and they grew those characters to be house hold names and to become more famous than Batman or Superman. Phase 4 is a new beginning with new characters and just like the new characters in phase 1 they'll grow to become household names.