WBFS is an easy file system. All management data can be held in a few megabytes. The block size is very large >=2MB. Writing an image to disc is usually a sequential write + 1 management block write. WBFS doesn't know fragmentation.
A FAT needs much more management time and writing operations for block allocation. If the file system is full or the image is fragmented, it takes much more time.
That's the reason for me to stay at WBFS. I use now the same WBFS drive for man years without any issues! And because of MKWii track testing, I create >300 image per year. With a second drive I went to FAT and after while back to WBFS again.