In none of those does explosive 'power' play a major part. The in-game Ho-103 has explosive bullets with significant explosive.
Maybe use of same word "power" by Oleg and Williams with different meanings has caused some confusion: Oleg means HEI content whilst Williams means an index (that does include HEI content, if any) of projectile destructiveness.
Although we don't have Oleg's values for Ho-103, presumably it should be similarly destructive to real rounds, like the ones we have. Indeed, I can recall only one P-47 victory that I got disintegrating target by its eight Brownings, all the rest being "suffered" like if the .50 would be poorly effective, but now I agree it's mainly matter of aim. In addition, I guess minor dispersion of deck mounted ones help significantly.