Been looking at the Revenant of Og’napesh and comparing them from normal to mythical, and the only change from what i can see, is a minor increase in damage…very minor.
There’s no more health or defense, no improvement in abilities, yet the level requirement
goes from 40 to 94 with no stronger pet ?.
Imo, especially since it’s an item-tied pet and can’t get skills from player,
it should gain new or stronger abilities and health when the tome increases in req lvl .
You are looking that on same character.
First of all 3 different level books have 3 skill levels, similar to regular investing skill in mastery pet.
This no obviously, but summon level (not skill level) scales with player level, and 94 lvl summon will be stronger on 94lvl than 40lvl summon on 40 lvl. There are also some unlisted skills that scales with skill level. You can see details on grim tools: Grim Dawn Pet Database
Thus, you can paraphrase your question to “Why is Og’napesh normal as strong as mythical?”