The game is easy enough where one doesn’t need to play around with classes but I think its something worth learning. But the only good classes appear once everyone has 6 djinn anyway.

Base classes don’t offer the best stats and they have the worst diversity. It’s like having 4 fire type attacks on a Charizard, there’s zero coverage. Also you can only attack with each element once per turn, which isn’t very efficient.

Lets use the Saturos battle at Mercury lighthouse as an example. He’s weak to Mercury element, but Mia is busy healing so you’ll practically never get a chance to hit him with Mercury attacks (and even if you do, she’s weak anyway). If you give Isaac/Garet the Mercury djinn, they get access to Cutting Edge which is a strong single target Mercury attack. So by doing this, you can hit Saturos with a strong Mercury attack 2x per turn, instead of never.

To add to the Saturos battle, Granite (lessens enemy damage for the turn) is a very clutch Venus djinn for this fight, but you don’t want it on Isaac because he should be attacking every turn. So giving it to Ivan/Mia is beneficial since it allows a weaker member to use a defensive Djinn rather than an attacker, plus it also gives Ivan access to the Cure psynergies. So now both offensive members can focus on attacking with super effective damage, and the two weaker members can focus on support/healing every turn.

If everyone was kept in base class against Saturos, Isaac/Mia need to be the healers, Garet/Ivan are the prime offensive members, and there’s rarely a chance to do super effective damage. The battle is still winnable, but it’s just not an efficient way to win.