That IS an interesting point; the revised DDC will focus more on NPC lvl (low, medium, high).
You could use an arithmetic progression for level - a L1 priest isn't easy to find (well, except for priest regents probably), but is surely easier to recruit than a L9 fighter who is happy to serve the regent - frankly at L9+ they should already have rank and position...
So for example costs might go:
L1: +1 DDC L2: +3 DDC, L3: +6 DDC, L4: +10 DDC, L5: +15 DDC, L6: +21, L7: +28 DDC, L8: +36 DDC...
To keep it simple you could reduce the number of steps - so a regent hires a low/med/high level Pc but doesn't know exactly what they will get
L1-3: DDC +5. L4-6: DDC +15. L7-9: DDC +25/30, diplomacy necessary, etc.
You can get someone at the start of their career under either progression method, but add mid level it starts getting expensive, at 'regent' sort of level it gets horrible.
The questions this poses are: 1) what should base DDC be? Should a bog-standard L1 or 2 fighter be a take 10 sort of action, or a toughie? Should magic be far ,far, rarer - and if so should that be reflected with a DDC modifier (as present), or just a 'the college/seminary produces 'x' candidates a year' DM-whim sort of modifier?
Should the current modifiers for magic, etc be subsumed into level barring realm spells? Spells, True magic, and Ritual magic assume high level already to be effective so I'm not sure it isn't double counting with the level mod to pull them out; but only the shift from 'adventure level' to realm spells is a 'step change' in power at domain level - and a paragon capable of casting such spells must already have some senior rank in a temple or a wizard realm to have got the practice of casting realm spells, suggesting that an adventure should be required, or diplomacy, or some sort of major recognition for an internal promotion.
'Don't think you can ping a realm spell person' is very necessary - as a priest regent I 'am' the ruler's go-to for realm spells, if the ruler could ping a moderate cleric then suddenly I have major competition... I'd rather it was a 'bribe the DM' sort of difficulty than a 'add 'x' to DDC' though - but obviously that puts more pressure on the DM team...
Personally I'd see different culture as a fluff thing - and likely a distinctly mixed blessing. An elf or goblin looey would cause havok in many realms... So increasing the cost by 10 RP (i.e. +5 DDC) seems unnecessary from a balance viewpoint although I can see the point - most hirelings, etc should be Anuireans because they are the locals.
The issue is 'advisers' - they probably wind up quite cheap under the above system as they have no magic, are low level, etc - even though they probably have a greater effect on domain-level play than any other hireling other than a realm-spell capable wizard/priest.
