I wholly and vehemently disagree that there was a "very fine distinction" in this case between murder and culpable homicide. I believe Masipa erred grossly in her evaluation of the evidence and application of the law when she found erroneously for the latter manslaughter-equivalent verdict. And the SA SC was pretty emphatic in the manner in which it slapped down Masipa's incompetence in its annulment of her verdict and its substitution of a murder verdict.
As you rightly say, there is (and so there should be) a certain amount of leeway for sentencing judges to take extraordinary mitigating (or aggravating) factors into account, in order to allow for sentences lower (or higher) than the guidelines. But to suggest that a crime which carries a MINIMUM tariff of 15 years' imprisonment can be mitigated down to 6 years' imprisonment (which, even if one adds in time served, amounts to less than HALF the MINIMUM sentence) is patently and arrantly absurd.
I feel extremely confident that a) the prosecution will appeal the sentence, and b) the SC will once again reverse the incompetent (or worse perhaps? Her repeated craven bending of the law in Pistorius' favour cannot but raise questions about probity and corruption, I'm afraid....) Masipa. And as others have said, using the "mitigation" that Pistorius' life is ruined etc etc is manifestly ridiculous: most convicted murderers generally find that de facto their life as they knew it prior to the murder has been ruined. It simply cannot have any significant material impact upon any lowering of the sentence. I can see that Pistorius' physical condition might be a mitigating factor, as might the sheer scale of his fall in the public spotlight (to a very small extent of mitigation) and his statements of remorse (albeit from behind a facade of claimed innocence), but IMO there are also significant aggravating factors including his actions immediately after the murder, his proven history of rage/control/jealousy towards women, his proven criminally irresponsible misuse of very powerful firearms (for which, let's not forget, he was criminally convicted), and his hour-long TV special interview coinciding with his apparent psychological inability to appear before the court for cross examination at sentencing.
Another important factor is that you are failing to distinguish or discriminate between those found guilty of culpable homicide in SA and those found guilty of murder in SA. The judicial fact is that Pistorius stands convicted of murder, not culpable homicide. And this, all by itself, renders comparisons with the likes of your other examples entirely moot. Furthermore, it would appear that the reason why others were (correctly) convicted of manslaughter-level crimes - rather than murder - was that the courts could not be sure whether or not these people were justified in firing their guns etc. While there was reasonable cause to believe that these people genuinely could have felt themselves in imminent mortal danger, there could never be a murder conviction. But the Pistorius case is different. The court (the SC, not the incompetent Masipa) ruled correctly that even by Pistorius' own account, and with regard to the physical evidence, it's perfectly clear that Pistorius cannot and should not have considered himself or anyone else in imminent mortal danger from someone behind a locked door - someone who by definition cannot have been verbally or physically threatening to Pistorius in any way whatsoever (since in fact it was Steenkamp behind that door.....).
I'm somewhat dismayed to read the stance you've taken on this matter. I think you're massively wrong. Time will perhaps tell, I suppose..........
Murder covers a pretty broad range of circumstances. For example, Rudi Visagie, the rugby player who killed his daughter, would pretty clearly have been found guilty of murder had he gone to court - he shot at someone he thought was stealing his car, when he was under no threat whatsoever. Yet if he had actually been found guilty of murder, I wouldn't have been at all unhappy had he received a suspended sentence, because of the magnitude of his personal loss. So the murder conviction in itself doesn't, I think, lead inevitably to a fifteen year sentence.
On your comment that "Pistorius cannot and should not have considered himself or anyone else in imminent mortal danger from someone behind a locked door", firstly, that's not very logical given that Reeva was the other side of the door and clearly in imminent mortal danger from him. But that aside, how fearful he felt is a matter of degree; there's no suggestion that he wasn't fearful at all, as anyone would be in the situation the court accepted he found himself. His genuine belief that he thought there was an intruder in the house and that he was under threat from that intruder, albeit not imminent threat, is clearly a very significant mitigating factor.
Only two of the cases I mentioned resulted in manslaughter convictions, incidentally; charges were dropped against the other two, presumably on compassionate grounds. However it's hard to see how a court could've been unsure about whether Tony Martin was justified in shooting, given that he shot the burglar in the back as he was running away.
Anyway, overall I think fifteen years would've been too harsh, given that this is someone who genuinely believed that there was an intruder in his house, as the court found. I think you have to set aside your own belief that this isn't true, and really put yourself in Pistorius' position that night to look at this with objectivity. That means considering his disability and the additional vulnerability he faces as a result, as well as the defences he's developed to cope with that. It means imagining how it would have felt to stand outside that door in the dark, believing there was an armed intruder inside, and knowing you can't even quickly run downstairs. It means imagining the shock and grief at discovering the person you shot wasn't a burglar at all, but your girlfriend.
What you can't do is look at this with the belief that Pistorius meant to kill Reeva but got away with it, and let your opinion on his sentence be swayed by that.
Don't know about an appeal. I suspect there won't be one, but as this case is seemingly never ending who can really say?