Let's see... Things that tiers could control:
- base wages. Irl your position is clearly visible, unlike hypothetical list of stats, and wage is based on it before everything else.
- max money income for jobs which have income. Even if you are skilled, low position can prevent you from using skills to the fullest. Perhaps with diminished returns, ie at some point increasing skills/stats becomes almost unnoticeable in terms of income until you raise the tier.
- clients "tiers" can be tied to chars tiers. Elite clients would like to be served by elite workers, and will be unhappy and leave otherwise.
- for warriors it becomes complicated because they don't generate income directly. It could affect available arena events and SE areas, you need high tier warriors to have access.
- equipable items and spells might have min_tier field required to equip/use them. This is especially true for weapons and spells, you can't just equip them and wear like some dress, you should know how to use them properly.
- skills can be limited by tiers directly, and become unlimited only at the highest tier.
Before we continue, are you going to use tiers for buildings/businesses? Or only for chars?
Because businesses can have tiers depending on average tier of used chars. And higher tiers attract better customers.