I am not sure if I understand you.

Yes, Research adds all your cities (and unit bonusses) from research additive upon each other.

I will assume you think that the research timer decreasing only 1 per turn is not working as you would think it would, correct?
If so: The timer only decreases 1 per turn because the total research time for the research (e.g. Leatherworking) is concluded from your total research in the top left corner of the screen.

Example (Math is obviously not correct): Let us assume you have 1 Research per turn. And you want to research Leatherworking. On Epic that would for example take 20 turns in total. The counter would then decrease once per turn.

Now if you enchant your city with "Inspiration" (from Water 1) you will gain 2 Research per turn. Leatherworking would then only take 10 turns in total. Of course: the COUNTER would still only decrease by 1 per turn, but it would only take 10 turns, not 20 anymore.

You are confusing two different numbers.  The "2 research per turn" means just what it says. The COUNTER is telling you how many TURNS are remaining to complete the item. Not how much RESEARCH is remaining. By definition, the COUNTER will always reduce by 1 each turn (because it is counting turns).

Observe that if you do something to go from 1 to 2 research, the COUNTER will change from saying "this will require 20 more turns". To saying "this will require 10 more turns". (However, it might not make that change until after the next turn update. I forget. So instead of being 19 more turns next time, ti will be 9 more turns. Confirming that research is being accomplished faster now.)

Another way to see this: cancel what you are researching and start something else. Compare the research the item required (in the lower-left city window) to the number of turns listed in the upper right counter. If your total research is 2, then an item that takes 20 research should be shown as needing 10 turns to complete.