That's why it should be balanced to be a higher time commitment then Dynamis. Also considering how expensive it will be to buy one 100 piece in Allied Notes if it takes at least a few hours of work, you'd be spending quite a bit of potential gil from the sales of other things.
What's the max AN you can get in an hour? I can do numbers based on whatever result you give me and calculate how much potential gil it could cost a player to go the 100 piece route depending on how expensive one would be. Ideally it would be a fair amount above the market value of currency obtained from Dynyamis.
I don't see why not since the new Nyzul areas are supposed to have it too. As long as the amount takes more man hours then the previous alternative it should be fine... if you have a limited amount of time you'll just do the older methods or Nyzul whereas if you have a lot of time on your hands you can slightly boost the amount you get in a given amount of time at the cost of it being inefficient against farming gil (or even converting IS into coins/VW stuff/attachments and selling those) to buy Alexandrite.
I'd also imagine that both of these would require a fairly high rank/medal. I'm sure people would appreciate having a nice reward for having the highest rank. This brings me to my next point...
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I think there isn't a big enough reward for the highest medal... I mean, you get weapons that only really work in Campaign Battle and a bunch of items that are broken outside of a Campaign Battle... so the reward for doing Campaign Battle is... getting better at Campaign Battle. I have a hard time giving my usual suggestion about similar latent effect items (such as Besieged and Assault latents) of making a key item that makes them function everywhere at 99 since some of them have effects like STR+25 on a neck piece - perhaps this would work but I really don't like to suggest things that SE might shoot down for balance reasons without checking it twice.
To give another unoriginal idea repeated again, even despite them being limited to Staff and Sword, I'd really like to see the weapon skills the Campaign weapons give have a questable component (perhaps such as "perform this WS 300 times" which would encourage more Campaign Battle). Perhaps to offset it other NPCs that do special WS could teach players everywhere how to use a weaponskill or even two... I know a Serpent General or two who has a weapon skill people would kill for example.
I'm sure I'll think of more obvious stuff to say that isn't exactly original later but there is just so much that could be done with the content to make it more equal with other options.