I'll agree with you, but that is a flimsy argument on thunder.
each element has it's ups and downs.
For water, your source is everywhere, water element jutsus are easiest to use when around a source of water, for example a lake, also it's easier after rain. Water jutsus aim to drown a person to death.
Wind jutsus have a continual source, and is used more widely in close range due to the sharpness of each attack, wind attacks are piercers, meaning they'll pierce through any attack, defense or a set of people even. Wind jutsus aim to slice and dice.
Thunder, it's fast, it's powerful, but only when concentrated into one pin point strike like Chidori or Raikiri. Thunder is much like electricity, it can flow throughout just about anything, it aims to stun an opponent or electrocute them. Thunder jutsus aim to stun the opponent to allow the user to input a killing blow.
Earth jutsus are defensive, they're not meant for killing at all, and serve as a perfect defensive. While it's weak against lightning, it's resistant to every other element, especially fire. Earth jutsus aim to defend the user whenever the time comes.
Fire jutsus are a strong offensive jutsu, while it may not serve as a great killing blow type of technique, it is certainly large, meaning it's better suited to fighting more than one opponent. While fighting with one opponent is not what it's suited for, it'll have better chances at hitting them. Fire jutsus aim to engulf their opponent in the flames.
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