seems to me that if you want just one winner and don't like the advantages that alliances create, the solution should be to go back to the old 2009 reWonder idea of disabling diplomacy altogether and perhaps sealing off the techtrade hacks by disabling diplomatic unit's ability to steal tech and disable the chance of gaining a tech when taking an enemy city.
wella: you would then have to research all your own tech and win by yourself. problem solved. (:
Hmm. I agree that removing tech trading would do a lot to reduce the need for massive alliances but I would hate to see tech stealing dissapear. Its one of the most important functions of diplomats and defence against the dark arts is as much a part of the game as defence against military units. However I would agree with making it more dificult and less one sided, with more risk to the player doing the stealing. I would suggest;
Higher chance that diplomat is lost when attempting to steal. (increasing cost of producing lots of diplomats).
If unsuccessful, a SMALL chance that the diplomat also 'defects' to the other side, taking one of the attacking players techs, or gold, with them. (increased risk of negative consequences).
I also think there IS a place in freeciv for capturing tech from cities. If its the only way to get technology then it will motivate the sim-citiers to play more agressively, or motivate others to attack the science farmers. So its not abused by informal alliances who repeatedly take a city to share tech, there should be a chance of techloss during capture. Something like 30% nothing happens, 40% tech captured by attacker, 30% tech lost by defender (So attacker doesnt get it either and War=Less overall advancement).