Separate Character Level & Class Level

[Nurvus]

Okay:
Synched Content
No noticeable difference, because Character level is also synched.
In Sastasha where requirement is Lv15 and synch 18:
Scenario 1: A Level 18 character with level 18 class (18/18) is as strong as a 60/60, because both character and class cannot exceed 18.
Scenario 2: A 60/15 is as strong as a 18/15, because both character and class cannot exceed 18.
Scenario 3: A 18/15 is stronger than 15/15, but weaker than a level 18/18, and maybe also weaker than 17/17 and 16/16 in some situations depending on differences in traits, skills and gear.

Non-synched Content
The only content where it makes a difference.
1 - Outdoor enemies will "recognize" your higher character level by allowing you to come closer without attacking you.
2 - Base stats provided by a high level Character make you stronger than a lower level character with the same Class level.
This doesn't mean you will have the stats of a level 60 character as a level 1 Class, since
a) the gear you equip depends on your Class Level
b) part of the base Stats come from the Class.
c) Traits depend on Class level
d) Bonus Attributes depend on Class level
You will feel more powerful than a newbie, but it makes sense, since at that point you're not exactly a new guy anymore.

In pure gameplay terms, it will merely make it easier and faster to level up, but that "difference" starts fading as your class level gets closer to your character level.
It doesn't make or break anything that really matters.