I know this is a feature, but I don't like the square grid. If in a next civ game you want some actual defense, it'll probably take a hexagonal grid, or it'll be far too ineffective. Diagonal movement as it is now should not be possible.This is not a bug. This is a feature of a particular strategic model.
Well, of course this trickle down occurs in the most extreme conditions. One condition would be that a tech only starts trickling down a big number of turns after your trading partner researched it. Also you could take distance into account. In the end, you'll probably be getting horseback riding in the medieval age if your trading partner went for it early, and techs like meditation and polytheism if you didn't go religious. It's not like your tech lead will be hampered, because the trickle down will be in so few techs (if the AI is at least not horrible), and they'll be so meaningless once they get them that it won't be a problem most of the time. Also, it needs open borders, so only your friends will probably get it.It depends on how it is balanced. If, for example, it were possible to beeline whatever line of tech development lets you get libraries and universities and science-enhancing buildings first (assuming no issues of Age advancement for the moment), then the amount of actual research you have to generate to catch up on the others paths is reduced significantly by being able to build those buildings before doing the research. Or if you beeline for marketplaces/banks/whatever, you can do the research faster because you are generating more trade overall.
I really, really do not like the notion that if one civilisation starts falling behind on tech it should get techs for free to keep it in play; that is actively penalising players who make the effort and play well enough to build a meaningful tech lead. If you get ahead you should have a meaningful and worthwhile benefit from it, and never being able to get more than two or three techs ahead is not enough. If what you want is to play against civilisations that can roughly keep up with you techwise, adjust your difficult level accordingly, but do not penalise players who enjoy the challenge of starting on a level playing field and getting meaningfully ahead and staying there.