Was the decision to distribute spoils made by the state or a council presided by the commander of the army? If it's by the state then i'd like source for thatCan you provide a source for your claim on Umar stoning someone to death for rape of a war captive? The only incident I have read is of him ordering the stoning of a soldier who raped a captive bride who had not been distributed by the state yet. So the sex was deemed illicit because the state itself had not given the captive girl to the soldier. Not because it was non-
Either way even going with the flow of your argument then even after being given to someone she'll have the status of a slave ergo she can't be harmed in any way, a slave girl was literally ordered to be freed by the Prophet himself due to being slapped, in another instance Abu Mas'ud was forbidden from beating his slave by the Prophet....the stance on raping a slave should be obvious taking all of this into account unless you bring an authentic and authoritative tradition/narration to back up your claim
And this is what a reputable Islamic scholar (Ibn Hajar Asqalani) said about Al-Waqidi's works on the ghazawat (battles): "He is acceptable in the narrations of the battles according to our companions and Allah knows the best."
Based on which criteria, methods of analysis and principles did Asqalani come to this conclusion? If you don't know (in case the acceptability of Waqidi isn't successfully established by you) then another question pops up, which part of your claim about Uthman from Waqidi is corroborated by other authentic sources?