Tiers as they are now are fine. Superman, Thor, Surfer, Orion are more or less on the same level.
Superman - can power a solar system sized machine on brute strength and absorbed a blast with his own body that was going to destroy the solar system.
Thor - can generate enough force to bust a celestial.
Orion - with the Astro Force contained a blast that was going to destroy the universe.
Surfer - can manipulate energies capable of destroying Galactus level beings.
So putting them on the same tiers is just logical. Tiers are about perceived average upper level to me, meaning that on average these characters would be a match for each other given their unique attributes.
I think story should take precedence over feats anyway, but trying to restrict a hero character's level in the comics is a fool's errand to me. Too many writers, too many perspectives.