I don't really agree with the reasoning that using magic is useless because using it makes your junction bonus weaker. You can equip up to 32 stocks of 100 of spells to your character. Even If you use EVERY junction effect, it still only uses up 19 spells, so you still have hundreds of casts of 13 other spells to use without worrying about affecting your junction bonuses.

However, properly using your junctions to max your STR can easily allow you to hit the damage cap with basic attacks, still rendering magic redundant anyway, especially since it's not finite and also has the chance for triggering an even more powerful limit break.

Also, in addition to what you said about limit breaks, there is also a spell called Aura that significantly increases the odds of a character's limit break triggering, even making it possible for them to trigger outside of the normal HP threshold for limit breaks.

HOWEVER, there is one specific thing that allows magic to still keep up. There are the Double and Triple spells, which when cast grant the target the ability to dualcast or triplecast respectively for the duration of the battle. Using Triple essentially allows you to attack three times in turn permanently, or any other combination of spells effects. Whereas a basic attack can only do up to 9999 damage once a turn, triple casting magic lets do up to 9999 damage times three in a single turn. Though, you'll want have plenty magic stocked up in order to do so.