As someone alluded to, the justification for doing this was added to the game when Augments came out. All you need is:
1) Speed Belt
2) Trusty crafter
3) Gigantic Brass Balls
4) Luck on the Augment
Put it all together and you could have a better than 6% Haste belt.
To me it's rather arbitrary if I could equip it 10 levels earlier, as all I care about is the best equip for my level 75 main job. I'm not saying I'd synth one myself, but 3 extra def makes it more valuable to me as a purchase rather than less valuable, as some state.
Worth less than Speed Belt, equipable 10 levels later, same haste boost. Just because someone was stupid enough to risk a Speed Belt for the synth, doesn't justify rougly +10M ontop the value of the synth mats.
