I'm not going to quote that wall of text but holy shit you're dense if you think there's no opportunity cost involved in giving items to members in exchange for DKP instead of selling them for gil. "But guuuuuuuyyyyys, I wasn't going to sell it anyways" doesn't change the objective value of any item or amount of time.

If an Ebody is worth 5M then it's worth 5M whether you sell it or give it to a shell member. You are giving them assets totaling 5 Million gil, typically at the expense of "DKP". Their DKP, which is a currency proportional to time invested, has a gil value. When you do a 1 hour event with the shell, you contribute 1 man-hour and are paid in the equivalent DKP. It's just money with a different name.