The current situation is that China's economic development and reform and opening up have enabled many enterprises to make profits through exports, which in turn has led to an increase in foreign exchange reserves. As a result of market economy, more foreign exchange will inevitably depreciate, just as you said. But from the literal meaning of "foreign exchange reserves", reserves are a means to deal with sudden demand in the future. So you can't stop saving foreign exchange just because you have more.
Why do you want to export, because you want to earn money from foreigners; And importing is to make foreigners make money. Therefore, import is one way, but it cannot be blindly increased. Didn't you see that foreign wine made all the money in China?
You are right, because foreign exchange is an international currency and can only be used for international transactions. Exporters earn foreign exchange, and those who want to buy raw materials at home can only be converted into RMB.