I've routinely found redemptions for $0.015 to $0.018 per mile on DL (which does factor in the 15% discount for being a DL AmEx holder) and finding $0.013 per mile is not uncommon at all. Now that has been for domestic redemptions (been a while since I've looked at int'l redemptions) but has been a mix of Y and F redemptions. I'm not saying this data point should drive someone's decision but simply saying better redemptions are out there and I evaluate both cash and miles options to ensure I'm getting an okay return. I generally won't consider using miles if the redemption rate isn't at least $0.015 per mile.

This isn’t a uniquely Delta problem, FYI. KE blocks all partner award redemption during their arbitrary peak times. Same issues on FB. You have to check their website each year to see when peak is. And it varies depending on region.