People pay millions to upgrade their gear to 61/63, which gives less of an upgrade than you get for free from that set bonus.
When you get campaign gear (or dread guard), you can put the armorings in any other light or adaptive armor and still get the set bonus, but until then, you have to live with the tionese-rakata look.
If I'm forming a raid and see that you lack the set bonus I will flat out refuse to take you, even if your gear is good enough for the content anyway since it shows that you care more about vanity then doing your job properly.
Is there any mathmatical theorycrafting to support your assertion? When I played WoW, people were able to make gear determinations by doing statistical analysis. I understand the desire to have best in slot in every part of your gear. However, sometimes that is more vanity then actual utility as well. I know people who would pay 1 million creditsd to change one mod that simply gave them 3 additional endurance (which is not statistically significant). Just for the sheer pride that it was best in slot.
I have been looking for, and and not yet found, tables that show how damage and mitigation scale and work.