I think the other person doesn't word it well.
First, the fighting isn't the main plot of the story, its more about everything in between.
The MCs are powerful, but still need to be careful in their fights. or they will die.
The story doesn't want dragon ball fights that are 20 chapters long, or have an impassible monster that de-rail the goal for 20 more chapters. Their obsticals are more about the world and people they interact with.
The magic combat system is pretty well thought out, but not complex.
The MC basically has lots of mana. That's their "op" trait. They developed a stragedy to spam cast the basic damage spell.
I'm making up some numbers here to kind of paint a picture of how this "basic spell" work.
Attack spell =
1 second cast time
1 damage to defence spell
10/10 damage to unprotected person. (Can do 9/10 depending on what the plot needs)
Can be cast in a variety of directions. (I.e it's not a gun, its a targeted missle)
cost more mana than the defence spell.
Defence spell =
.5 second cast
Can absorb 100 hits
low mana cost for small area over a short period of time, high cost to do "full coverege". Its essentially a sheild they move around and resize to block attacks as they come. Fully protecting yourself burns too much mana and you'd lose.
For most hitting the defence spell a hundred times is a stupid stratagy, so everyone came up with different spells that break through it in a few hits.
Out MC instead trained the basic spell so much, they can cast it 20 times a second over a long period of time. This forces the opponent to burn mana trying to maintain defence. The opponent is overwhelmed and get hit. However the stratagy only works if they back the openent into a postion where they can't counterattack or have a buddy attack MC from behind.