"more mild" is correct and can be used in written English.
For example, you could say, "The weather today was more mild than the day before."
The Romney campaign's position is more mild.
On its surface, more mild weather could sound like a good thing.
More mild reactions include dizziness, headache, gastrointestinal stress, irregular heartbeat, and heart palpitations.
But even there, the critiques have been much more mild than what I've experienced here.
Bush was not caught lying, and in comparison to Trump's language, he was substantially more mild.
"I'd like to see something a little more tempered, a little more mild.
And people with more mild depressions get better with just about all treatments, including placebos.
There's actually a much more mild 7.4% increase between 1990 and 2011.
But yesterday's volatility was much more mild as investors took a more cautious tone.
The Southeast, Plains and Mexican-border states, as well as much of California, will likely get more mild winter days.
The 2012 version shows that planting zones have been shifting northward as winters become more mild.
