As it is said just because you are paranoid doesn’t mean everyone isn’t after you.
I think his gripes were mostly with the Valeban, and with Dorna whom he thought quite likely correctly were out to nobble/handicap him. I always agreed with your view of the tyre wars way back when but don’t recall Casey ever complaining about tyres when he was with Ducati, and he was hardly loathe to complain. He did make comment about both the late weight change and late tyre change for the 2012 Honda on which he had been streeting the field in pre-season testing and him specifically asking why winning 5 titles in a row on a Honda was OK for Mick Doohan while he had to be stopped after one title, hence it looking to him that him winning, whether as a rank outsider or riding for the establishment marque, was unacceptable in general. I also think from reading stuff in the Australian press as well as his biography that he considered he had proven what he wanted/needed to prove by winning the second title, and that continuing to prove the Valeban etc wrong was not a sufficient motive for him to keep going. He was also upset prior to Honda with Ducati whom he considered family for not supporting him when he had his health issues.
I also agreed with your view back in the Ducati days that after a race where he had balanced on a precipice/knife’s edge for a whole race he had a let down from all the adrenaline post race and was prone to not saying anything particularly sensible. When he is interviewed these days nearly 20 years on he still does the pressure of thought thing though, so perhaps that’s just him, and in general he was probably simply not suited personality wise to the limelight.
As for his general character who knows ?, but Shuehi Nakamoto spoke highly of his character, and Dovi said he was a different person as a test rider for Ducati than when he was his totally driven team-mate at Honda in 2011. There are people even in Australian bike racing circles who never liked him though, and I recall one Australian poster on here in particular back in his very early days. I haven’t seen or heard anything anywhere from him critical of his parents though, and I don’t think there was any path for him other than the one he and they took, bike racing being quite a minority sport in Australia. I am sure his family didn’t mind the fortune that came his way eventually, but they also had this kid with obviously ridiculous talent/natural aptitude who was beating older riders before his teenage years, rather than it being a similar deal to the father of Tiger Woods or the Williams sisters, or the parents of several other tennis prodigies.