I want to be very clear here: the problem with this is NOT the timeframe, or the difficulty. It's the deletion of player progress.
I will HAPPILY grind against really hard challenges! I will grind for WEEKS to achieve something hard. But I will NOT spend 12 hours a day grinding for something only to lose it all because I only got to 90%.
As someone on the forums said, it's even fine if it's just degrees of failure! If things varied between 'Total Loss', 'Major Loss', 'Slight Loss', 'Stalemate', 'Slight Victory', 'Major Victory', and 'Total Victory', and I'm able to push it from 'Total Loss' to 'Major Loss', at least my work is being recognized. It's totally okay if we're not meant to make much progress in the war right now.
But if all my work is just gonna be deleted, I'll just log off and wait until they lower the challenge enough for my effort to matter. Simple as that.