Hello,
Grade Penalty doesn't modify your stats. The problem is that the XML skill has only 1 level.
I changed it to 10 levels and it's working.
<skill id="4267" levels="10" name="Grade Penalty">
<!-- A penalty applied when the grade of equipment one is wearing is not appropriate for one's level. -->
<table name="#rate">0.22 0.19 0.16 0.13 0.1 0.1 0.1 0.1 0.1 0.1</table>
<set name="target" val="TARGET_SELF"/>
<set name="skillType" val="DEBUFF"/>
<set name="operateType" val="OP_PASSIVE"/>
<set name="castRange" val="-1"/>
<set name="effectRange" val="-1"/>
<for>
<mul order="0x30" stat="pAtkSpd" val="#rate"/>
<mul order="0x30" stat="mAtkSpd" val="#rate"/>
<mul order="0x30" stat="rEvas" val="#rate"/>
<mul order="0x30" stat="rExp" val="#rate"/>
<mul order="0x30" stat="runSpd" val="#rate"/>
<mul order="0x30" stat="regHp" val="#rate"/>
<mul order="0x30" stat="regCp" val="#rate"/>
<mul order="0x30" stat="regMp" val="#rate"/>
<sub order="0x40" stat="accCombat" val="20"/>
</for>
</skill>