Why does Frieren only use basic spells when shes supposed to be one of the strongest mages?

Rewatching season 1 and something keeps bugging me. Everyone talks about Frieren like shes this legendary 1000 year old mage, but in almost every fight she just fires Zoltraak, which the show literally calls ordinary offensive magic now. Is there an actual in-story reason she sticks to the basic stuff, or is it just so the big moments hit harder?