tu_79
Deity
See it this way. There are eight civs in the standard map. The first six civs took freedom and order. No one took Autocracy. The fifth civ gains five free tenets.You're suggesting the status quo, more or less, which does nothing to prevent a mad rush for one ideology or another, once the first-in bonuses are gone. And the rush is because of the large unhappiness penalties if you choose differently from the culture leader. (There's also the rich-getting-richer issue.)
With Gazebo latest, had the player change ideology, he would lose all five tenets.
Edit. You're right about the unhappiness issue for those that come so late, though. They would be forced to change. So maybe the unhappiness for not following the cultural leader could be tweaked down.