The spell charges in FF3 seem quite balanced yes. I usually beat a boss just before I'll run out of high-level curing, or use all/most of my low level curing just before the boss appears.

In FF1, DoS was an adaptation of the easy version from origins, or at least it seems so. It may not be. The leveling is fast, like origins-easy. Supposedly the strength increases are spread out over the levels for the characters to compensate, so that a 40 DoS Fighter is equal to a 20 NES Fighter, but I find it isn't quite that linear. Spell damage is also fixed to about 75% of its value, making the randomness of 10-40 fire spell actually hit for 32-34 now all the time.

But to talk more about it would start a FF1 topic.
FF3's charges seem just right. I'd want more, but these get me by for now. Well Red mage's charges aren't anything to wish for.