So between Thursday night and last night, I went from the start of Ch2 through to the end of the NG+ playthrough. Which isn't to say that it was smooth sailing, especially with the new Alt Missions and NG+ exclusives, but... yeah. It really, really is all about overwhelming firepower. I wonder, if I wasn't
so annoyed with Sea Spider showing up 3 missions after Balteus with no additional parts being made available, how many knocks upside the head it would've taken me to start playing around with the Impact stat. I generally favor bazookas and missiles for first playthroughs anyway, and they have pretty decent Impact ratings, but... oh well!
Anyway, NG+.
First, the Arena - only 9 extra opponents there, surprisingly. I would've initially assumed that this second half of the Arena would be, like, the "real" versions of the 29 opponents - but it's not. There's Alpha, Beta and Gamma versions of the same robot, and 2 also-rans for each. Went 1/1 on all 9 of them, some were taken out in as little as 20 seconds. The
possibility for them to be dangerous is there, but by the time you reach them - even if you're not using a stolen build like I am

- you definitely have a loadout and skill set that trivializes them.
There are 3 slots remaining; those will definitely unlock in NG++. But it's noteworthy that killing these 9 reward utterly ridiculous amounts of OS Chips (basically Skill Points to put into things like Energy Weapon Damage +15% or Damage Taken -15%), and once you've killed all 29 original fights + these 9 Analysis fights, you have all of the OS Chips necessary to max out every category.
Second, the original missions - pretty sure that, indeed, none of them changed at all difficulty-wise. Some missions get straight-up replaced, some have dialogue options that change who you fight, some are simply listed as "Alt Mission" out of the gate. There are also "Decision" missions, which were there in the first playthrough, and... god
damn did I luck out. I didn't fight the Cataphract, the Redguns or (Ch5 spoiler)
betray Carla and Walter - if I did, any of those, without all of the OS Tuning (and to say nothing, again, of the "overpowered" build), would've been a nightmare. Ch5Spoiler and "Liberator of Rubicon" penultimate and ending bosses were fucking wild, and I think all 3 boss encounters surpass Ibis Series CEL-240 in difficulty... which
is saying something.
But, I don't have context for whether your second ending's missions get buffed up or not. Probably just safer to say that Fires of Raven -> Liberator of Rubicon (NG+) -> True Ending (NG++) is the best course of action. I think I was just correct with my initial assumption that the higher mission rewards on those Decision missions indicated how difficult they were, and that choosing the one that pays less was the best course of action.
Finally, all those new quirks that are exclusive to NG+. There weren't any more "clearly Armored Core" missions like the ship escort or Junk Robot, so still basically sitting at just two fully realized legacy-style sorties unfortunately. Can't really see NG++ adding much of anything on this front, but we'll see. The battles added in were, thankfully, not Soulsborne in nature either - just more ACs (and, more importantly,
groups of ACs) that fight normally. The biggest ones are definitely squaring off against two major story NPCs in an Alt Mission, and another in a replacement mission that starts with you fighting two of the highest ranking combatants from the Arena and then a special, and incredibly dangerous, third AC shows up partway through.
At the moment, I would say: I don't have any feeling of pride and accomplishment. I cheated not only the game, but myself. I did not git gud.
...But there's some measure of fun and entertainment in using this zoomzoom shot-zooka monstrosity to be on a more even playing field with the incredibly inconsistent difficulty. Even when I'm failing a mission/fight 3~5 times now, I don't
quite feel like the game is cheating me or otherwise being impossible and unfair. I just need to be mindful of a certain attack, or maintain a certain distance, take one specific target out before the other(s), or be a little more precise in aiming.
But that, again, really is just because I'm using the weapons everyone has discovered offer the best Stagger-shredding capability. There's simply no reason for 90% or more of the weapons in this game to exist, especially all these things with like 3 Impact and 60 Attack Power. The Zimmerman shotgun, for reference, has 840 Impact and 900 Attack Power and unlocks after you kill the Sea Spider and move into Chapter 3.