Simply saying don't need FDIs but getting them is better.
In a way but not entirely.
FDI is essential to how China developed besides simple financing. Foreign direct investment (FDI not FII which goes into equity like stocks) is how China leapfrogged up the technological ladder.
The work force that trained under the JVs in every industry from toys to PCs to autos to aircraft allowed China to moved up the development ladder far faster than any other developing country.
Tesla in Shanghai we already spoken about. But another prime example is the Airbus FAL in Tianjin. The work force, processes and standards introduced there uplifted an entire industry that will reach in a decade what we are seeing in the car industry today. Confidence to generate 1300 orders for the C919 comes from an eco-system that includes some of the best practices of the leading manufacturer in the world today.
So even if you not need the money (which is evident since China is capital excess country and invests huge amounts in the BRI alone) it is still essential to continue getting foreign investment so you do not develop in a bubble -- which the West wants to restrict you to.