If you ask me, Def is the worst stat to invest mag levels in. You get +1 DFP per level, where a DEF material provides a permanent +2 DFP. Technically DEX is the worst stat a mag has (+1 ATA per 2 DEX levels). However, there's no such thing as an ATA material, so DEX becomes the most valuable mag attribute.
I've hand-calculated a couple plans for you based on potential goals.
For the first plan, I tried to replicate the stats you quoted at the top, using only the character you mentioned.
Second, I put together a plan assuming you would use this mag as a level 200 tech user, using this
guide as a baseline. I also assumed it would be fed from 5-200 only on your mentioned character. I also tried to find ideal PBs.
I hope this helps!
By the way, did I menton I love mags?