What is worse, many civs have the same basic techs about things that appeared thousands of years prior. I would use a "rename" if that's what the corresponding civs actually developed, and the impact would be comparable. What worries me a bit though is that, for example, Persians and Seleucids would have almost completely different techs, since one completely preceded the other chronologically. Should their techs be just a rename? Should Seleucid techs be better, but more expensive? Should, as someone proposed somewhere else (with some problems), some civs turn into others (sometimes with choices) along with their Phases? This last thing would solve lots of historical accuracy problems, but would change the game in a fundamental way (maybe something to test on some mod).