As a fan I never actually allowed myself to truly accept that I didn’t like the film until I started getting a sense of the ROTJ that could have been - obviously guys like Larry Kasdan and Gary Kurtz and Harrison Ford have come out in favour of Han’s sacrificial death and a generally deeper/bleaker finale.
I am still surprised when people are bringing up Kurtz when it comes to ROTJ. He was fired and replaced by Kazanjian in the middle of ESB principal photography. He basically had nothing to do with ROTJ, let alone being aware of any details such as Kasdan’s and Ford’s suggestion to kill off Han. He basically just jumped on the “ROTJ should have been darker” bandwagon years later, while probably still being resentful of his removal from ESB.
Now considering Kasdan’s and Ford’s suggestion, killing off Han would have not have made the story and the film magically any better.
I’m aware that the Kurtz thing is speculative in the sense that none of us can know exactly how/why things broke down between him and Lucas. My guess is that the truth lies somewhere in the middle - Lucas was annoyed at the cost overruns on TESB and Gary was less than thrilled at the direction SW was going in. But the general feeling about ROTJ stays the same - many folks involved felt that ROTJ was too light or didn’t do justice to its predecessor. Even Kershner apparently read the ROTJ script and said he wasn’t feeling it.
Well it is extremely likely that the main reason why Kurtz was replaced was because of cost overruns during ESB, as you mentioned. But by the time he was replaced, any kind of form of ROTJ story/script was at least a year away. So I guess the only direction he could have been “less than thrilled at” by that point, was the direction until ESB. He might have read ROTJ script later on (like many other people), but that is judging in retrospect without being involved, and therefore cannot be the reason for his departure during ESB, as he likes to claim. We all know Lucas did not have anything pre-written as Lucas himself likes to claim; he basically wrote story and script for both ESB and ROTJ only after SW and ESB were released, respectively.
It’s not that killing Han was the answer. It’s more that killing Han (or having him die a noble sacrificial death) was something quite a few people were down with, and that in itself is an indicator of what people were feeling in terms of giving the story some weight generally.
After you invest two and a half films developing romantic sub-plot between Han and Leia? That is not “giving the story some weight”, that is giving the story a slap in the face (as Ray put it).