My current impression is that peacock is the undisputed best character
I feel bad for linking a random twitter thread here and dragging other people into it, especially because the thread involves a private account, but here's SonicFox saying that they think Ms. Fortune is the best character. So at the very least, Peacock being the strongest character is not undisputed:
Regarding the rest of what you said, I'm mostly just concerned about correcting misinformation. But I also worry because Peacock is a projectile zoner, and most modern fighting games' solutions to balancing projectile zoners is to intentionally make them underpowered, or at least to make it so they can't win by zoning and have to go in a lot, because more players tend to get frustrated by playing against projectile zoners than other archetypes. So attempting to balance the characters for "equal frustration" would likely either result in Peacock being underpowered, or Peacock losing her projectile zoning focus and becoming a more generic character design.
As for the Robo comparison, Robo is a beam/poke zoner whose main strength on point is that she has no weak spots on the screen so she can zone very safely, and she requires a specific type of assist to unlock her full strength and get big damage from beam conversions (e.g. Annie H knuckle and Annie pillar DHC). Whereas Peacock needs to stand on the floor to throw projectiles (which can be very hard to do in a game where brass and giant step and Beo sweep and Parasoul bike and ringlet spike and a million other ground-level anti-zoning tools exist), so when she manages to do that, her reward is stronger. In other words she has bigger strengths but more exploitable weaknesses, meaning that people who have no idea how to play the matchup or exploit her weaknesses will have a harder time against her.
So Robo's "shoot lots of weak beams from anywhere" character archetytpe is inherently a less annoying type of zoner character to play against than Peacock's "throw projectiles from the ground" archetype imo, and that applies even more to people who don't learn character matchups. There's a reason that a low-frustration beginner focused game like Guilty Gear Strive was perfectly happy to include Axl, but they didn't include any heavy projectile zoners like Venom or Justice or Dizzy (who was kind of a zoner in +R but I was struggling to think of a third example lol).
There's also a huge difference between Robo just being at the back of a team for the beam assist, and a team built around enabling Robo strengths as the "main character". Robo is (in my opinion) easily the weakest solo character in the entire game, which should show how much she relies on good support to be strong on point. Anyway, Annie is the perfect support character for Robo-focused teams, so I'll be interested to see how frustrating people think Robo is when they start having to deal with teams that can hitconfirm from a falling air H beam into an Annie DHC for over half of their health. Peacock, on the other hand, has been the "main character" of most zoning teams for a very long time, and most players probably have experience playing against teams that maximize her power.
Anyway, sorry for another big message! We're probably mostly in agreement here, and I think that Peacock could/should still have a few more nerfs. I personally like the idea of nerfing her defensive options a bit. I think I already suggested making her projectiles disappear if she's hit by a non-assist non-projectile attack (although that could end up making H teleport useless so maybe certain projectiles such as sHP cannonball should stick around?), and I assume something similar to the Annie beta's assist + H teleport nerf will be tested again in the next beta cycle. I just think that the end goal should be to make her a competitively balanced character while also nerfing the most frustrating aspects of her are unimportant to her core fun (e.g. projectiles breaking combos, M bang previously being very hard to punish on block), instead of making her zoning so competitively weak that it makes up for people's innate frustration with projectile zoners.