#1 E5 is a "sync byte" it cannot be rotated and mis-interpreted: E5 E5 E5 ... can be used to synchronize a bitstream. Note that floppy discs are read bit-wise.
#2 Empty 8" floppy discs came pre-formatted with E5 written everywhere.
#3 05 is a "control-e" in "extended 8 bit ASCII (IBM encoding)". E5 was a usable character.
With CP/M, the disc bitmap was produced when the disc was "loaded". All directory entries were scanned, and the allocation bitmap was produced. A freshly formatted disc would have E5 fill, and thus would have no files. MS-DOS had a separate allocation table, which was also the file linkage table. So, the strategy of a fresh E5 filled disc being taken as empty no longer works. But, the key of a deleted entry having E5 as the initial character was still used.
Hope this helps.