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I don't know about the speed of the memory and of the SSD yet, so I cannot affirm it is worse than in the current Air. I don't know why Thunderbolt is so important, I don't find any use for it, and I don't care about it.
This laptop is thinner and lighter than the Air, and it has a better screen. Of course it has advantages over the Air. It may have a slower processor, and that is to Air's advantage, but not everything in the Air is superior.
Yes, no need to try to argue re: RAM and SSD speed. RAM speed essentially doesn't matter now that CPUs have multi-megabyte caches. This has been the case for years and is proven by basically any real-world benchmark testing. And any SSD speed over a couple hundred MB/s is fairly pointless unless you're doing something very specific that requires that speed, which most people certainly don't.
I would also argue that the size/weight differences between the Samsung and current 11" MBA are insignificant. A small fraction of an inch and a small fraction of a pound.
The difference in screen size is also fairly inconsequential. Remember than the 11" MBA actually has an 11.6" screen. With the amount of bezel it has, it could easily accommodate a 12.2" screen with zero changes to the form factor.
So basically it boils down to the Samsung having a better screen and the MBA having a more powerful processor. And also being significantly cheaper. So I'm reluctant to say that the Samsung is a clear winner here.
Of course ideally Apple will release an "11 inch" MBA with a screen similar to the Samsung's and not too much of a price increase. I imagine it will happen sometime but only a few people know when.