You really don't know what honor means, huh.
It's not about being rational, or efficient, or about utilitarianism. Quite the opposite. Being honorable is often deliberately worsening your chances of winning - because that's not what's important when you're being honorable.
If all you wanted to do is win, you'd resort to every underhanded tactic in the book. You'd win more fights; but it wouldn't be HONORABLE.
And that's the whole point here.
Going all foh honnaahhh on Sylvanas and then sneaking around behind her back sabotaging and conspiring is NOT honorable. It's an efficient way to usurp her power, to be sure - if that's your goal, by all means. But don't pretend it's about honor when you're not acting honorably.
Nobody said being honorable is a particularly smart thing, in terms of achieving victory. Those who care about honor care about HOW you achieve victory, and would rather suffer honorable defeat than dishonorable victory.