Just because tech trading (and tech path) is the most important decisions you make in the game (besides DoWs) does not inherently mean it's overpowered or game ruining. There's an option to turn it off and as far as I can tell most people rarely turn it off. If it was as simple as it giving you an unfair advantage I'd turn it off all the time because I'm a masochist.
I wouldn´t go as far as to say TT is game ruining, but game limiting/narrowing pretty much; as you are compelled to do so copiously to get on par within any game running the feature.
Again, don't believe it as unfair as other players will use it against you too (never mind the human outplays the AIs, this happens at every level of decision making). But TT does in fact umbalance some aspects of the game (buildings being the OP issue of the day), which would otherwise be very much good to go.
Agree on the concept of niche building. Many players tend to disregard the oportunity cost and specially the build order (possibly due to playing on a very comfy difficulty level I pressume); thus getting little reward for the effort.. but clearly a bad call in the first place.
One other thing Drewis, decision making concerning the tech path becomes thoroughly a matter of developement, as technology ceases to be a common trade good of multiple value (2x, 3x.. 5x

) So TT economy is no more. Dead. In fact, out of the blue, mind process changes too. You no longer choose tech revolving trade at all, your only focus being domestic growth/military, and any plan along them.
Does my country need to enter the iron age (IW) and risk not to get iron immediately or do I start the path of aesthetics->literature-> drama (you know the drill..) to get some of the wonders and the cultural buildings, and keep defending with chariots and archers? Risking to get DoWed in the middle of the process.
May I rather develop my wealth towards guilds & banking or do I aim to education and try to get liberalism, since I surely won`t be getting both for the price of one. Countless examples of the sort.
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Slower speed games exacerbate decision making here, as you´ll need 15-30 turns to get some techs, depending on map, economy, developement, war/peace.
If you plan to bribe an AI towards DoW (and grab the many benefits) you will have to spend the cash, many times the cost of half a tech for instance. It will hurt of course, you no longer get to gift away the cake and eat it as well. So on so forth.
CivIV takes a grip on balance when TT is off. Just saying
