What I hate the most about technology research in these types of games is that some players just fall so far behind in tech that it's just not fun to play as them or conquer them. Such players have such an inferior army that everyone hates them, and either makes them their slave-nation or declares war on them. These tech-challenged players have little influence in diplomacy or in warfare.

I would really like to hear what others think of this issue and what they'd do (how to fix it or leave it alone).

I understand that it makes more sense that the faction that does more research should be allowed to tech up faster, but it comes at the cost of you or enemies becoming insignificant over time. I was considering research becoming efficiency base, i.e. tech per population. What would you do? How?