This is a perfect example of "pigs get fat, hogs get slaughtered". When ESPP shares post, sell them immediately. Regardless of tax treatment. This example is perfect for this. Regular income tax on the 10% sure is better than taking a bath on a stock that's gone into the toilet. Because I sell ALL shares.....ESPP, options, RSUs immediately, I was able one quarter to pay off my mortgage, buy my wife a brand new car and get myself a $2000 TV. My co-worker (a hog) poo-poo'd my selling, saying it was going to skyrocket because it had dropped over the last 2 years. Well, 4 years later, the stock had not gone above the strike price (I sold at 3X the strike price) and he was let go. So I got my mortgage, car and TV and he got squat. To boot, his ESPP shares LOST him actual money.
Do what you want, but if you're putting too much emphasis on the tax treatment, be prepared to be slaughtered.