Reminds me of some of the disappointments from Star Trek.
Nicolas Lacarno becoming Tom Paris or Kira Nerys replacing Ro Laren, for example.
Those were minor adjustments to minor characters but it still ticks me off to this day.
I think those changes were for the better in both cases. They ditched Locarno, not just for creator-rights reasons, but because they decided Locarno had been too unrepentant and wasn't ultimately a redeemable character. And Ro wouldn't have worked as well as Kira because Ro was a Starfleet officer, meaning she would've been required to obey Sisko's orders. Sure, she wasn't above questioning orders, but actually defying them would've cost Ro her job in short order, so she wouldn't have been able to be as strong a foil for Sisko as Kira was. Also, Ro didn't believe in Bajoran religion, so she wouldn't have been as effective a contrast to the Starfleet characters in that respect either.
To me, as a writer, it's surprising that so many laypeople see it as a "disappointment" when one idea is replaced with another, as if that were some kind of failure. On the contrary, it happens all the time in creativity; the first stab at an idea is rarely the best one. Even if you're required to abandon an idea for reasons beyond your control, it can still give you an opening to come up with something even better. Because the more obstacles you face, the more creative you have to be to get around them -- so in a creative field, obstacles are opportunities, not failures. (I mean, heck, George Lucas's plan A was to get the movie rights to
Flash Gordon. When that didn't work, he made up
Star Wars instead. Was that a disappointment?)