Antenna gain and coax loss are absolutely factors in station performance but line of sight, dictated by antenna height (HAAT) will be the dominant factor in a given station's effective range.  No amount of power or antenna gain can manufacture range, only height can do that.  Yes, enough feedline loss could ultimately overcome signal strength and effective range.  But factoring typical system and path losses for a basic V/U FM station, you are far and away better off to have a high antenna with some feedline loss vs a low antenna with little feedline loss.  

Mark K5LXP
Albuquerque, NM