Interesting take on grouping popular sizes into more sensible ranges.
The chart you use though uses screen sizes, not view port sizes. Are you assuming everybody browses full screen? 1024 x 768 may very well be a desktop user.
That doesn’t have to be an issue in practice, but it can. Some developer may make the conclusion by the name “tablet portrait” that he/she can or should do some touch-only or touch-optimized thing, which would be an incorrect line of thinking.
I like your ideas, just not the device names. I’d still prefer XS, S, M, L, XL as a naming scheme.