I think it was said you could research down multiple paths at once.
Tech assimilation shouldn't be guaranteed, and probably should be fairly rare, without plenty of trade, and some level of technological parity or progress.
I agree, for the most part. I mean, how low is our tech to begin with? I'm sure we will already have basic things.
But here I'll use this example.
You start trading with your neighbor, you use small 2 wheeled carts hauled by a single horse as your engineers are to brain dead to think up a better alternative. Your neighbor gets twice as much goods moved in half the time with his multi horse 4 wheel carriage. Obviously It would not take long for you to adopt that tech.
I also believe that there should be a chance, however small, that warfare tech can be passed during battles. If you see the enemy fight and it is superior to your ways, assuming you survive that battle you are going to focus on mirroring or countering there way of fighting. This should give you a tech or atleast decrease the amount of time left on your tech.
There are SO many ways tech can be discovered, your researchers can be givin the spark of imagination seeing how the rest of the world does it.
In fact, they should make sure that you can set up a "Research treaty" which will allow scholars and engineers from your empire travel to your allies and observe how things are done there, sort of a cultural/technical exchange program. 