I would say that this somewhat ties into a S1 relevance discussion as ftp could be the group most reliant on S1 heroes. There are maybe a handful of top 100 alliances that would take a true ftp player (“maybe” because I don’t know all of their recruiting requirements).
I see these as the biggest roadblocks for a true ftp to join a “typical” top 100 alliance:
Troops - multiple high level troops, a longshot to have these.
CoK/MT - requires resources or specific rosters to satisfy meeting minimum requirements.
Rosters - can require specific heroes, emblem counts, sheer numbers.
A couple years ago, I could see an avid ftp working their way into a top 100. Not so much anymore.