Just giving my two cents here, without reading any of the thread responses:
Arbitrations feel unrewarding. Not that they don't give us rewards, but in the time it takes the game mode to do so. Waltzing around for 40 minutes to get a bunch of Endo doesn't really feel like Endgame. Arbitrations feel more like a game mode that would lead us into Endgame, with mods like Adaptation and Rolling Guard being in there. But then the rotations feel so long and boring that it doesn't feel worth it. Maybe making Defense and Survival tolerable time-wise, but reducing the amount of endo per rotation (and chances, in the case of mod drops) could help alleviate that? It'd help people ready up for whenever what endgame is gets figured out, leaving a good foundation for when it finally comes.
The mode itself isn't inherently bad, although the drones feel like artificial difficulty sometimes. Maybe giving them the Scrambus/Comba/Ancient treatment and creating different types of them, for varying effects. It'd need good visual feedback, so we don't get any more units as infuriating as any Energy Leech eximus, but it'd add variety instead of making us play Duck Hunt 2: The Final Frontier with the drones because we literally can't kill or CC the enemies affected by them.
The reviving mechanic feels more like a crutch to include newer players into the mix. The sentiment isn't that bad of a thing, but should a thing announced as endgame be so accessible? And then the fact that you'd have to impair your survivability, the most important thing in Arbitrations, to try and save someone who, most of the times, just wasn't ready to be there will just make public Arbitrations into a salt-fest with people complaining for you to revive them because they died 3 minutes in. It doesn't feel even close to endgame. It feels like babysitting someone who wasn't ready to do it, even though it's called endgame. And since this is probably going to be shipped anyway, at least make it so burdens aren't picked up like Index points. No one wants to debuff themselves by accident and then have to walk around potentially being the next one to go down because of it.