Okay, here's the deal on tech rates.
Early civs have research penalties relative to later ones. These penalties, which are present in vanilla RFC, are generally larger in our mod. Byzantium, for instance, starts out with a huge number of techs which no one else has, as well as a large empire. They have to be strongly penalized in research or they would always dominate the game. Similarly, we want the Arabs to fall behind in tech around the renaissance, so they start out with extra techs but have a slower research rate. The details can be adjusted in RFCEBalance.py, which is reasonably easy to understand. I encourage anyone who is interested to play with some of those parameters. If you come up with some changes that seem to preserve balance and realism and make it more fun, let us know.
I believe that when the AI evaluates the "value" of a tech in a trade, there is an asymmetry. If you offer the AI tech A in exchange for tech B, the AI (cheating a bit) looks at how much if would cost you to research tech B, and how much it would cost them to research tech A.
Tech A might cost you 1000

, and Tech B might cost you 750

, so you think it's a good deal for the AI and they should take it. But if your Civ has tech costs which are twice as much as those of this particular AI Civ, then the AI decides that Tech A would only cost them 500

to research, while Tech B would cost you 750

to research, so they're not going to do it. This mechanism, incidentally, is why it's hard to make "fair" tech trades in vanilla Civ at Monarch+ levels.
Anyhow, I agree that this sets up a confusing and frustrating situation for the human player. I will play around with narrowing the tech cost gap (handicapping early civs in other ways).