I've got, allegedly, a powerhouse of a private sector, no income tax at all, and yet my economy has been stuck on 'imploded' for months. No matter how pro-business my decisions might be, it won't budge off 'imploded'. Do ratings ever get, well, stuck?
I think the "Imploded" is probably based off of your GDP per capita (which according to NSEconomy is only $105.72) where the "Powerhouse" is probably determined by your overall GDP (According to NSEconomy once again is $150,438,473,284.04)
I got the information from http://nseconomy.thirdgeek.com/nseconomy.php?nation=Bunglord
Just keep trying to get you economy back on track it might take a while though....