Agreed. There should be alternate legacy paths for Antiquity and Exploration (Modern Age is already locked in because of the Victory Conditions). The game could randomly pick between 2 legacy paths for each category. That way there would be some replayability from game to game since you would not know which legacy path in advance.
I remember workshopping a bunch of potential legacies before the game came out when I thought it would work more like the Humankind stars / achievements than the paths we've currently got.
Antiquity
Middle Ages - Complete Future Tech and Future Civic.
Baqt - Have 3 Alliances.
Monopolium - Have every copy of a specific resource within your borders.
Koinon Symmachon - Be Suzerain of every existing City-State while no Independent Powers exist on the map.
Alexander Wept - Have a Commander with 3 Commendations.
World Capital - Have a City with 50 Population.
Exploration
Padron Real - Uncover every land tile adjacent to coast, and discover every Natural Wonder.
Voyage of the Beagle - Control 2 Natural Wonders in Distant Lands.
Sun Never Sets - Have a City with at least 10 Population on every continent.
Invincible Armada - Have 2 Navy Commanders with at least 2 Commendations each.
Third Crusade - Conquer and convert a Holy City in the Distant Lands.
Age of Piracy - Capture 5 Treasure Fleets from other Civilizations.
Company Rule - Integrate 3 City-States in Distant Lands.
Thirteen Colonies - Have Distant Lands settlements produce more combined Production and Gold than Homeland settlements.
I also think it would be cool if there were some 'Dark Age' style legacy paths. The Dark Age concept in general is sorely underused in 7. What if losing your original Capital triggered a unique '''bad victory''' milestone? What if there was a 'Government in Exile' type route if you lost all your Homeland Settlements in Exploration? I really wish the Dark Age legacies were actually gamechanging and worth spending all your points for. It would be sick to have a rough Antiquity, then turn into a giant Mongol Horde in Exploration to get revenge rather than just quit.