No, I do not agree, because it is not so.
Putative private defence is where there wasn't an actual threat, but one
mistakenly believed one was acting fully in lawful private defence where one was in fact not. It is that simple.
If one knows the law, then subjectively one must have believed the requirements of private defence were being met, including the force was necessary and proportionate. The response to the threat is therefore assessed subjectively. Eg If one knew he could just close his front door and protect himself from what he thought was a charging attacker outside, but instead chose to shoot him, then on a subjective assessment of his response, he did not in fact act in putative private defence. The subjective assessment may mean he intended to unlawfully kill, and may well be guilty of murder. If this assessment was only ever objective as you contend then he could never be found guilty of murder. It should be noted that putative private defence can even in theory be a mistake in knowledge and understanding of the law relating to private defence, so the listed absolute and specific requirements are not necessarily so. Even knowing the law, one can kill in putative or actual private defence even if one did not believe one's life was being threatened, e.g. you thought you were going to be raped and the force you took was necessary and proportionate to ward off that attack. Your formulation and descriptions of the strict requirements for private defence aren't exactly correct, e.g. what i just said, e.g. 'no possibility of escaping' - case law shows you don't have to flee your own home. The true descriptions are contained in my previous post from Professor Le Roux, Jolandi, Private Defence: Strict Conditions to Be Satisfied (May 3, 2010). Journal of Contemporary Roman-Dutch Law, Vol. 73, p. 328, 2010.
http://www.websleuths.com/forums/showthread.php?241098-Theory-Thread-What-happened-at-Pistorius-house-on-the-night-of-Feb-13-2013&p=10892008#post10892008
To be found not guilty of murder in a case of actual putative private defence, one must not have recognised and accepted the risk that one may not in fact be acting in lawful private defence.
To also be found not guilty of culpable homicide in a case of actual putative private defence, one's beliefs and conduct in relation to the killing must also have been objectively reasonable based on what a reasonable person might have done.