What AZ says, tech trading benefits human players early cos of Aesthetics and other known trading key techs.
But later, when teching towards Gunpowder/Mil. Trad. and/or Rifling, how often do you trade for stuffs like Nationalism..CS..Paper..Edu?
Phi leaders become overpowered, be it for GSpies or bulbing everything important, not worrying about later cos you know with hordes of Curis you can always end games..AIs will never reach Rifling in time.
Be that as it may, normal-speed deity games with tech trades off are incredibly rare on the forums.
Tech trades are fundamentally broken. You have no other option in game that gives >100% returns (POST multiplier!) on investment in the game. A comparable bonus is the 50% from bureaucracy, which requires high upkeep, gives less bonus (by a wide margin), and is limited to a single city. The primary drawback is that an opponent receives your technology also, but ROI from trades with multiple empires dictates that it is still best to swap techs by a WIDE margin.
Nothing else can touch tech trades as a factor in gameplay. People use them to instigate AI wars, to secure gobs of gold (then turn around and talk about how
multiplier buildings suck, as if that would still be the case w/o broken features), to buy OUT of wars, to secure people from attacking, and to increase tech pace at a rate that *literally* nothing else in the game can touch.
Despite assertions that NTT makes the game easier, there's little-to-no definitive proof of them.
When I see tech trades and research agreements, I see a trump card so powerful that it overwhelms many of the other decisions made in the game. It's so strong that if possible to do so people virtually always trade tech.
Do you always HA rush? Do you always go music early? Do you always research BW as the 3rd tech? Improve tiles in 1 way? Use religion? Use corporations and/or state property? Use siege?
No. It crosses a line that no other un-nerfed feature could dream of reaching, and yet it chugs along in some form in every single game. An equalizer, and a powerful one at that.
. There are precious few things in any civ (or TBS for that matter) where one feature among many can so readily and soundly overpower other decisions/outputs.
cost to 
yield and the 
from one doesn't stack with the other, so you can really punish cities if you want the units quickly. We argued over it earlier, but I find ~30 rifles and 40 cavalry to be > 50 cavalry or whatever you'd get from only whipping cav, and having the cavalry is MUCH better than pure rifles (which I'd not only advocate if you lack horse).
