If Rael decided to use Rui's breakthrough to the Apprentice Realm to its absolute fullest, then the stakes for both sides in the war skyrocketed. A greatly enlarged supply of Martial Apprentices meant that in the future, Kandria would greatly surpass all the other Sage-level powerhouses in the quantity of Martial Artists.
In other words, it truly was do or die at that point in time before the additional supply of Martial Artists made a genuine difference.
"Martial Apprentices cannot affect the strategic outlook of an all-out war."
Neither of them had any delusions in that regard.