The devaluation part is a bit more complicated. There are legitimate reasons for a country to want to devalue its currency. Yes on the one hand it can be considered exploitative because it cheapens exports and allows western countries to get global south goods for cheaper.

But the imports part is a bit iffy. The thing is the ‘well off’ within these countries import a ton of high value added luxury goods from the west. Sure, the country gets the good but the foreign currency could instead be used to purchase capital goods (tractors to mechanize farming for instance) that increase domestic productive capacity. By fixing the exchange rates, the Government is using publicly owned foreign currency reserves to subsidize such consumption. Yes there are alternate ways a country can prevent this such as import duties or trade restrictions but people often find ways around such restrictions. By not fixing exchange rates or widening the range, the state can prevent the private sector from using state resources to subsidize their consumption or capital flight. The state can still use price controls, subsidies or provide favorable exchange rates to state owned companies.

Of course, many a times these countries are forced to devalue not because of any trade pressures but because of capital flight or excess external debt. IMF comes in and forces the country to devalue rapidly instead of in a controlled manner which would have allowed the country to adjust better, remove price controls on essential goods like fuel, privatize & cut Government spending in general.