I figure it's better to base on the total points of Abilities, since that is primarily what the characters can do. Base Zero, that is, having Weaknesses within + or - 5 points of the Ability total, is more of a character creation balance, so that doesn't really apply to the character's power level.Ineffective characters have 0 to 4 total points in Abilities. They just do not have the power to affect the world.
Minor characters would have 5 to 9 points, and are generally notable NPCs, who might have some skill and strength, but generally cannot do what protagonists do.
Average characters have 10 to 14 points. While not superhuman, these characters are still good at what they can do, and in a low power setting can be the main heroes.
Heroic characters have 15 to 19 points, and is recommended for most action or high power settings. These characters are the adventurers in guild, or the party of pirates that take center stage.
Major characters have 20 to 24 points, and will be, well, major players in the world. The kings, guild masters, high wizards, generals, and the like.
Supreme characters have 25 or more points. These would be the gods or the Big Bad of the setting, and occasionally the heroes that rise up to the insurmountable challenge.
I am basing this off My own observation of a character with 15 points in Abilities makes a good starting hero, and a character with 10 makes a good low power hero.
I haven't tried it, but I am thinking that a group could use the range for a bit more variety in points. For example, if the GM wants a Heroic game, one player could have 15 points in Abilities, another with 16, and another with 18 points, and still be about balanced with each other.
How does these tiers look? Is there a nuance I am missing? Anything I should add or take away? This is a rough draft of the idea, so everything here is up for discussion.