If he had done it in front of everyone? In front of all the rest of the Horde? I imagine that even if she refused it, it would absolutely divide the Horde in a more believable way than this.
Those who still believe in the old ways would have seen her openly show her true colors and sided with a Saurfang they could actually believe in, because he challenged in a way that is fairly sacred and respected by most and an open denial would have been seen as unworthy of a sitting Warchief. And those who are diehard Sylvanas loyalists wouldn’t have cared either way because they were already on her side and willing to fight for her regardless. That would have been a more realistic divide than what we got. I’d have joined his cause in a heartbeat after witnessing at least an ATTEMPT.
Instead I am asked to choose between a leader who is increasingly proving to be evil or someone who abandoned his people, was entirely willing to sit the whole thing out after two failed suicides and is ONLY coming back to rebel because the enemy -allowed- him to based on their shared cause.
Horde isn’t fun anymore and won’t be no matter who wins.