I have noticed that you can unlock era 6 without researching tech past era 3. My suggestion is that the 9 techs needed to level up is from the previous era only.



So era 1 - 9 techs researched - unlocks era 2



era 2 - 9 techs researched (from era 2 only) - unlocks era 3



era 3 - 9 techs researched (from era 3 only) - unlocks era 4



and so on.



I hope this is taken into consideration as I think this would improve the progression through the game.



Rugroll

The reason why they did this is to allow more freedom for the player to research things by priority, cuz some eras have things you might not need depending on if you are focusing on Industry+Food VS Dust+Science



So for example, playing as Broken Lords I decided to research all the Dust and Science technologies from era 4. But I only researched 5 techs from era 5 cuz I don't really need the Industry for Broken Lords. I still managed to get to Era 6 thanks to the freedom to prioritize whatever suits my play style and faction.