Assassin's Creed Unity runs poorly even on SOME monster machines, while some have a luck of having just the right configuration combination that it works. As for Far Cry 4, it is reported that game uses only one core, or it mainly uses one and uses other cores very little to none.
That said, currently your 2.1 GHz probably won't do it (at least until it can use all three cores). Also, RAM and GPU won't serve you good. I agree with you man. Thats the same case for me. Yesterday Ubisoft released patch 4 for Xbox One & PS4.It says it has fixed fps, lag and companion app issues.
The same patch will be released for PC but will take another week. So will see if it really improves on low end systems.
If you are like me you are probably using a dual core processor to play Far Cry 4. As we all found out, it does not work:( But there is a solution, to use an injector to basically trick the game into thinking that you are using a quad processor.
But for me, I tried this many times and it did not work. Thankfully I have found a way to fix it. If you are like me you most likely bought the game off steam. When you do that you also make a Ubisoft username and so forth.