[Shujin]

I agree that the downside is sorta small for Duo-destiny so I was hesitant to actually suggest it. But then again you have the downside to not swap classes on the fly like some people do, to adjust to a situation and actually have to stick to your guns. Thats actually a big downside (Granted, not even half as big as Full Destiny but yeah.)
Thats why I said if we had Destiny only skills they certainly won´t get those, but I guess working on the premise of something that doesn´t even exist is probably bad.

Uhh your "Level guide" doesn´t work out though for a good part since those quests are quite limited and you can´t even get those 5 full inks for one class if that would be a thing. and you probably need 10 to "Max" out your two classes. Also auto assuming you have friends to let you piggyback ride them is a bad concept over all for a game and doesn´t really say "Grinding it easy" but "getting levels by others is easy!" which is true, but not speaking for grinding on your own. 4./5.) sounds more like an exploit, but I guess it works.but you do all of this like 5 times and yes, no matter what you tell me, it´s a huge boring pain in the ass no one really likes doing, thats why I am not a fan of that idea to be honest. But I can also agree that "Duo-destiny" is maybe a bit lackluster in it´s downsides over normal destiny to be valid as a thing, as much as I would like to use the classes more to it´s fullest for more funzies.

So I guess the "Fairest" option would indeed be the grinding.