If you tell your characters to disagree, it is impossible to have an outcome where one doesn't win and the other loose.
If you don't want the characters to disagree, either set the AI personalities to loyal or leave them unset. You can also disable dual dialogues between the main characters in the options. Leave one main character far enough away that they are not involved in the conversation, and there is no chance for them to disagree.

Why would the game show ties in single player RPS? Would adding pointless rolls so it takes longer make it a better mechanic?

There is a mod to reduce the frequency of NPC comments. Quiet Day On The Market

Before insulting other peoples' intelligence, perhaps you should consider how your level of articulation presents your own.