Every source I ever found that mentions the CW-21 says that it is capable of climbing at at least 4800 feet per minute which works out to be 24.3m/s which is much more than the 18.2 on the stat card
https://assets.ctfassets.net/4wrp2um278k7/7GOXWtoNQBfVKJCV8cqKLy/b4abc3db529d0ea16c4f9d18cfcc8948/Inkijk_Warplane13-.pdf - scroll to the last page