User blog comment:Miskos3/Fairy Tail Chapter 488: The Two of Us, Always, Review/@comment-73.191.17.103-20160609020656/@comment-7418318-20160609151149

Come to think of it, until now nobody addressed what good killing August would have done... and the answer is very little.

Sure August is freaking powerful, but does Alvarez really need August to win? Or to put it better, can Alvarez only win with August?

The answer is no in my opinion. They not only can win, but are still almost asured to win even without August. The army with Zeref is many times bigger than the one defeated at Magnolia and in the south... and they have Irene too (unless she dies to Acnologia who's presence is as of yet unknown to Mest so shouldn't enter any of his considerations), who Brandish reliably told them to be close to August's power-level.

Tl,dr: Even if Mest had succeeded it wouldn't have helped the war-effort much and ruined any chance of a peaceful resolution. A gamble with minimal chances of success, high risk and little possible gain.