Did you just arbitrarily pull those numbers, or do you have some basis for weighting them so?
I am not familiar with the rankings system on wowhead, but it seems that by creating a value for armor that is the same for stamina you have grossly overestimated the value of armor. One think to keep in mind is that you gain much more armor per item point than you do other stats. For instance, 100 item points might be granted to 100 dodge rating, or 150 stamina, or 1000 armor. Now, I'm not sure, but I've seen other sources say that armor is alocated at 1:10, sta at 1:1.5, def/dodge/parry at 1:1.
If that is the case, by inputing armor as 300 you are likely overestimating the value of armor by at least 6x that of stamina. My numbers might be wrong because I don't know the system on wowhead, as I said, it just strikes me that that would be a problem you might encounter.
All that to say, Cloak of the Shattered Sun is still one of the greatest eh pieces in the game. There could conceivably be situations in which it would be more beneficial.