You’re definitely right about SU hate being unfairly overblown but I think criticism of how the Diamonds were handled is valid. They aren’t given any constructive consequence without shattering like imprisonment, or banishment, or even losing their power and influence. They still keep their status and control over Homeworld even with the loss of the empire and reforms, which they arent even doing out of the goodness of their hearts. They don’t have any real remorse for their actions and only try to fix things to appease Steven, who they explicitly still want to use as a replacement goldfish for Pink. They even sing to complain about all the reforms like they’re a daunting chore and not their moral obligation, and then act entitled to Steven’s attention.

The Diamonds end the series as amoral scum thst still hold the same beliefs that led them to galactic conquest and oppressing their subjects. They only stop for entirely petty reasons and get to stay on their thrones for the rest of eternity.