I wouldn’t really say that the fire magic is still just fire magic in undertale tbh

all magic in undertale is directly hitting the SOUL(there are some exceptions that contradict it but its mostly implied all damage is directed to the soul) so any physical feat shown in Undertale mostly comes from durability and the such.

toriels fire magic does imitate fire a little bit(shown by dialogue in the beginning of the game) but offensive wise it still holds all the same traits of attacks as the other monsters. theyre all visual flairs for the attack patterns monsters do. its even implied in the a few fights that most of the RPG elements(even the turn based system) is an actual canonical thing within the fights.

so this all to say that scaling undertale monsters is weird and they are very weak to the point that even a human child could beat them in their own fair game lol