Well, I wouldn't call it "unbalanced" nor would I use this argument against tech trade.
Firstly, in what way "unbalanced"? Some alliances get ahead more than others? Well, with no tech trade it also happens that some players get ahead of others and it also doesn't depend on skill. It will mostly depend on who your neighbours are and if you get lucky with bribing idle settlers.
Also, even if you call it unbalanced, like someone said, that's how world functions. Multiplayer is not singleplayer. Cooperate or die. Successful "alliance leaders" will recruit everybody whom they can, the argument "I don't have time for diplomacy" doesn't stand, you just have to say "yes" when asked to go into alliance. And yes, it will depend on whether your neighbours are also cooperative or not, but everything else also depends on it, so, tough luck. Civilization isn't a fair game. No massive multiplayer game is.
And most important of all, like someone said, if you lose tech trade, you lose an important layer of the game.
All that said, I strongly believe that tech trade should go hand in hand with tech upkeep. I don't understand why nobody is playing with it already. I did a test game with default values from the Multiplayer ruleset, got to industrial age, it worked just fine. It smooths out, but doesn't eradicate, the difference between big and small nations, disables technically backward neations (no libraries, low Sci percentage) to receive high-techs. It is somewhere between "no tech trade" and "yes tech trade", how close to either depending on the numbers, and is basically an excellent compromise because it takes best from both and nullifies some downsides.