i genuinely enjoy Fire I, Fire II, Fire III
like actually naming the spells implies they're actually different spells that have been individually discovered and perfected by different mages. like there's someone who specializes in fira but she *can* cast firaga, which is objectively the universally stronger spell as determined by all the information the player can see, so fira mage forgeted herself by dedicating her craft to something that is obsoleted utterly by something else
the idea that this fire mage specializes in fire spells in general and just knows when to use fira or firaga is more probable to me then an actual visible difference between fire mages, fira mages and firaga mages
unto the spell's nomenclature itself i think it's really grounded and down to earth to just have a forgetin number, like some mage saw this and was like 'ok that's weak fire' and then saw another and was like 'ok that's stronger fire' and started calling them by their relative levels of power instead of a more arbitrary 'greater fire' or 'master fire'