This is what I have to say regarding Dark Aeons:

Dark Valefor has a measly 800,000 hp. I only had 90 strength for Auron and Tidus with Yuna at 95 magic. Ifirit and Ixion are also easy as I beat them with 125 strength/magic.

Yes it is easy to get dark matters. Just overkill like 60 hornets and its done. So ribbon is easy enough to aquire. Just get BDL from celestial weapons. I agree with points made by both Tavrobel and vivi_ultima but luck is useful.