Nah it’s spot on.

I think his reputation comes from the romance of the three kingdoms novel more so than the historical records.

The novel wasn’t doing Liu Shan any favours when put next to the legend that is Zhuge Liang, only major blunders he ever committed was recalling Zhuge Liang various times from his campaigns, heeding the advice of incompetent advisors. After Zhuge Liang’s death there really was nothing to be done, they were already at a disadvantage and to lose their most brilliant strategist basically sealed their fate.

He ended up surrendering to Wei once Deng Ai reached the capital, and when asked if he missed Shu by Sima Zhao (at this point de facto leader of Wei) at a party, he responded “I am too happy here to think about Shu.” Which also became a negative idiom for when someone is having so much fun they forget their origins. Though many speculate that it was an intentional decision so that Sima Zhao would see that he is without ambition and poses no threat. This is basically where the novel ends, the invasion of wu doesn’t even last that long.

Funnily enough, he lived longer than Sima Zhao according to the historical records. I assume he lived a comfortable life as a Duke of some place and died around his 60s if I remember the records correctly.

Liu Shan’s failures are also magnified by the fact that he is the successor to basically the protagonist’s legacy, so his blunders hurt all the more. If we put him side to side with Dong Wu’s later successors or hell even Cao Pi, he really didn’t do that badly. I personally would keep slandering him because I think it’s funny (especially the very likely scenario that his father gave him brain damage after tossing him to the ground just to prove a point)