Ok this is an idea.
Basicly an Onion Knight will start of with low equal stats.
Ie lvl 1 will have something like:
STR 5
DEX 5
VIT 5
INT 5
MND 5
CHR 5
it will have 2 lvl 1 ability
Healers Shift
Attackers Shift
You can only set 1 ability to the ability list, which has points set to them. (Like Blu with there magic)
The ability shift can only be changed every 12 hours, after first been set.
Healers shift will grant boost in mp and mnd and the list of white mage spells (not all whm spells just most of them like cure status remove and bufffs etc..)
Attackers Shift will have Stats boost to HP VIT DEX and STR
Also as you level up ie say lvl 10 you get job passive ability like DEF Bonus, Attack Bonus Magic DEF Magic attack etc...
Which can be set using the points.
And job ability's like provoke boost and other job ability's that has to be set by the points again.
You can change then as you see fit, but there will be a waiting time before there can be used.
At high lvl you can unlock other shifts like
Magic Attackers Shift <--- BLM sort of magic and stats
Mighty Shield Shift <--- Tanking sort of job.
Each higher level shift will cost more points to set.
The idea is to offer one job that some one can change to suite there needs or to full a gap in a party.
This is just a rough idea.