For example, you could imagine bracket one has cards that easily can go in any deck, like Swords to Plowshares , Grave Titan , and Cultivate , ...

Swords to Plowshares, which is currently banned from Historic and will probably never be printed into Standard again, is in the lowest power bracket? Am I misunderstanding the purpose of these brackets?

I know one-for-one removal isn't as good in Commander as it is in two-player formats, but even so. Adding Swords or Grave Titan would noticeably raise the power level of every Commander deck I've ever built. Apparently my decks are in bracket zero.