To be fair, they were numbered back in classic FF games (I-VI and I think VII?), and an easier way to note the difference could be the way XI did it. Fire for single target, Fira or Firaga for aoe. But yeah, spells such as Flare, Break, Flood, Tornado, Freeze, and eventually Ultima, Holy, and Meteo/Meteor (if those are implemented) need to look powerful. Fairly quick to keep the flow of battle going, but still powerful.