Nova on release was a much different frame and I would say the first iteration of room nukes. Her molecular prime was not duration based, so it would instantly affect things in its range so both the effect and explosion were range based. This is pretty significant since now you usually don't build for range because of narrow minded and her 1 is actually more useful if the null stars arent beaming enemies. 10 years ago was a different game with a different power level but she was pretty much sayrn on crack since it was a slow + 2x damage that scaled etc.
And I don't know how misinformed you are about nezha's capacity to "only kill weaklings" and "not very strong". The augment was insanely broken as it was 50m non los armour strip cc if built right ON TOP of everything nezha does - damage vuln, 90% dr, iframe on halo cast AND break, fire walker providing cc cleanse, and usually roar/nourish. He has no problems killing anything in 1hr+ SP. No other frame in the game does as comfortable as nezha does and thats why it was nerfed.
Every frame you listed has to have some sort of interaction to nuke things. Equinox has to ramp and is squishy, Octavia has to maintain her nocturne or she'll just die from a stray bullet 100m away, mags crush is 18m for armor strip but polarize is base 8m with pulse travel time so its pretty much like nezha's augment now, Gauss's thermal sunder is like 10m or 12m i dont really remember, Lavos has actual cooldowns, Mirage outside of ESO isnt using discoball or ledgerdomain tech as the main nuke for anything more than 20min. Revenant aoe builds usually have some kind of conflict with his comfy roar build and you have to do some major min/maxing to have everything in one build, but its still balanced around the fact the beams have some weird oscillation and it drains energy. There was no balancing or downside to nezha's nuke. And no they probably didn't care for initial testing because nezha probably has like a 5% lifetime playrate and practically no one uses him if they either have rhino (easier to get) or revenant (completely immortal). I'm a nezha main but I think its delusional for people to complain about the nerf. It's in line with what DE usually does to "nuke" like abilities, and in fact they know they could have made it worse. In the changes they said "We didn’t want to change the Mod in a way that would alter the functionality that makes it so effective" because in the past they would usually change the damage, change the scaling, add los, add a cap, or just change the ability completely. The mod still does the same thing, but now you might just have to bullet jump one more time which is totally fair.