My understanding is that Sharapova was intentionally legally doping before, the rule changed and her team didn't update her regime. I feel less sympathy but at the same time, I'm sure legal doping is common and it's a bit of a grey area anyway. With Halep, I think it was a contamination issue but in larger doses of something she was taking so it 'may' have enhanced performance, even if she didn't know. If we take Sinner's statement at face value it is a bizarre case. His physio cut his finger and decided to use said cream on his finger for a week or so. Not long after applying it, he gives Sinner his massages which gets into his body through skin lesions.
I think there are some key differences in cases but like you say the messaging, timings and process just seems unclear. Even if everything was done correctly for Sinner, it seems that consistency has not been applied throughout and even if it has, the perception of consistency is not there either, which presents an issue in itself. If the system doesn't feel fair, there's something that can be fixed or tackled to address players, fan and media concerns.