The punishment isn’t just the $5,000, it’s the public shaming that came with it. You’re not going to be able anyone’s name here for many years without this case coming up. The world at large has been watching this unfold gleefully.
That, combined with the lawyers involved having decades-long clean slates, as well as this case being outside the normal realm this team would operate in, as well as ChatGPT being relatively new at the time this happened makes it all seem pretty proportional.
Maybe you could say they deserve worse for how they handled things after they got caught, but I struggle to really have a problem with this punishment considering the records of those involved.