The mathematics you speak of is just a metric, one metric of many, that is used to measure whether or not X feature, Y boss fight, or Z item is "balanced" in the scope of which it is relevant. With enough observation of the gameplay you can mathematically determine where things fall short, and what could be deemed as overpowered. Balance encompasses many things, and i hate to say it, but the "experience" is a large part of it. Without a balance, certain rules, techniques (skills, abilities, etc), or even complete segments of the game can be deemed ineffective, worthless, or at the other end of the spectrum, gamebreakingly overpowered.
This is part of my major gripe with modded minecraft; with such a large swath of mods, so many different developers visions of what is and is not balanced, and even within the same mod some things are ho hum or take it or leave it, and other things making you feel like you *must* progress down X path and forgo the rest. It kind of ruins certain parts of the "experience." and this is why balance is always subjective, because everybody has their own idea what is and is not.
edit: both paragraphs can be taken as two separate thoughts/posts. balancing a modpack is very different than balance in civilization or skyrim. as in, it's near impossible.