Been driving manual all my life, I had a BT50 2009(mazda) in my country for my daily driver and shifting was smooth af... for a 2013 car, designed by MB, I can tell you that the jerky transmission is not due to my technique. I have seen a lot of people complain about it here and it seems it's either you get used to it or it magically disappears after a few miles. Mine has 17k miles so you would think it be optimal now. I solely drive it on manual and the shifting is really not the best (for a 2013 car). I wish I could fine a solution for this. I heard the 2016 model does not have that problem, which I could swap the pertinent components
I don't think it's you either; there are ways to make it less jerky, but I think that's just the nature of it and changing it involves investing significant time, effort, and money altering it.
Swapping I don't think would be realistic. One can
do a lot of crazy things and make things fit (Project Binky), but for the time, hassle, and money I think it'd be easier to sell the 451 and buy a 453, or perhaps, pardon my heresy, get something else. Not knocking the car, I love mine, but it's not for everyone.