I feel like it's a system built on strong-stronger-strongest tiers, which doesn't work too well for me because there's no sense of gravitas to each tier. Dragonball Z offers the closest comparison I have offhand - they go super saiyan, but then there's like double saiyans and ultra saiyans and so on, with power levels that go over 9000 and - it kind of stops making sense after a while, just a matter of who has the strongest will. It's okay to have powerful magic, but there's a difference between video game magic and book magic - VG magic is usually numerical, where Geralt can't use the persuasion spell on this NPC because the difficulty check was higher than his spell power could overcome, whereas book magic has to rely on cause-effect. Full Metal Alchemist's opening conflict involves the two brothers trying to bring back their dead mum, it costs main character an arm and a leg, and ghosts his little brother so he has to possess armor to have a physical form anymore. That tells us it's really hard to resurrect the dead - so we have an idea what the "cost" of spell casting is going to be.
Here, it kinda seems like you could keep self-applying runes as long as you have the body space to do it, and they'd work for a good, long while (however long it takes the tats to fade/sag, it seems) but since the "combat focus" appears to be in physical strength and dexterity, book smart isn't even a requisite - just start with the light opening rune, add a bunch of muscle runes, and boom, unstoppable juggernaut.
And one of the MCs doesn't even need tats - just the words of power passed down from the divine language? So she sacrifices nothing to gain everything. Mm... kaaaaaay.
Geralt's spells may not be very well defined in terms of cost, but we do know he was emotionally crippled, rendered impotent, and suffers amnesia every other tuesday (it seems.) We also know other Witchers tend to go crazy and become monstrous themselves (hence NPCs being like, "Ew, a witcher? Gross!"), and that his five spells are really puny next to Yennifer's or any actual witch's magic. But that's the thing: he has five specific spells and can't really learn any others. His toolbox only has a hammer, and suddenly, all his problems look like nails.
But if your protagonist can have any rune, which does anything from a minor healing cantrip to a major city destroying typhoon, and the only catch is self-inflicted scarification... how am I to believe any stakes or consequences she comes across when I already know she knows the divine power language?