@N4mm1nh
Prestige was probably the wrong word to use, I was aiming more in the vein of 'significance'. The more relevant a character is to the current story the more powerful they are/become in relation to everyone else. This is how a character introduced in chapter 600 can be stronger than any foe up to that point, even though the new character has comparable feats to enemies defeated 300 chapters ago. Admittedly the author has done a better job here by not making Shin succeed at everything on the first try or making many his successes simply survival rather than victory, but the power-related hand-waving when introducing new characters is still pretty apparent.
In terms of simple physics you may also be correct about the armor vs boulder argument, meaning that if 'Power' is equivalent specifically to 'Strength' rather than 'Ability to Slice Objects' you are correct. A general built like 3 oxen stuck together with gorilla glue is more likely to have enough 'Strength' to cleave 12 armored individuals than a small girl is to slice a boulder. But if it's possible to apply enough technique, speed, precision, and lesser amount of power required to make your weapon into 'something that can cut any object regardless of hardness', this feat is less likely to be repeatable 12 times in rapid succession. I feel that many of the feats we see are somewhere between these two definitions of 'Power', with the blunt-weapon generals and the Shiyuu representing the extremes of both ends. I don't see the boulder slice as any less believable than a club going THROUGH multiple people like a baseball bat through birthday cake, as we've seen sevral times. Both ruin my immersion, but the last time I read Kingdom to be immersed Shin was still figuring out how a sword works.