It was established long ago that level 6 of lucky charm resulted in fewer magic items than level 5. I looked through all patch notes and could not find mention of this ever being corrected.

Is it still the case that 5 lucky charm is ideal?

Reference thread: How Lucky Charm works

Pretty much, and lucky charm is still terrible overall. Like anyone gives a crap about green items past level 7. You can easily edit the treasure table if you want. I improve lucky charm treasure tables in Scales, my mod (see main forum.) You could download the mod and just use the treasure table (though it does also make all mini-bosses (like the Lighthouse boss) drop epic+ items and reduces the white weapons/armor you find by half.)

Thanks! I've looked into your mod before but hadn't considered using only certain parts of it. At level 15 I'm a little too far for some of the more radical changes, but I'm using your treasure table now which will hopefully alleviate some of my boredom during the tedious late stages of the game where every fight feels the same... At least I hope level 15 qualifies as "late"... Must finish... before I can let myself... play... Xenoblade Chronicles X...