There are ancient magic equivalent for grand fire curses.
Inferno & Scorch both have ancient magic equivalents, check this A current list of all known Lost & Ancient Magic , he also has brought it up in the discord.
If you’re talking about the known ancient magics then its just that we’ve seen these magicsi n the game, they were mentionned ingame, or are really obvious choices for future ancient magics/ are already present in some way
Inferno (Warren)
Death (Morden)
Equinox (through clash reactions)
Electron
Apocalypse Bringer (Nero)