I don't see the big deal really. Unless you are playing a weird guide or power gaming chances are Phoenix will be the last esper you obtain with the possible exception of Ragnarok and Crusader. Thus making the extra growth only useful for getting secondary party members up to speed. Chances are a few members have already learned Fire 3 from Tritoch and god knows Terra should have naturally learned that spell by then.

Also, I'm not surprised a "flaming bird" can teach a fire spell faster than an Aztec god that's more associated with thunder. The elements given are usually associated with the deity the esper gains its name from with a few odd exceptions... Besides, Maduin is unique cause he teaches the basic level 2 elements all at once even though there are a few other espers that can teach them. Tritoch is unique cause its the only esper that teaches Ice 3 and Bolt 3. I don't see why Tritoch should be treated as an upgraded Maduin.