You put this in D&D, so I'm responding strictly in that context. Also, this breakup of class and subclass (as opposed to rangers being a subclass of fighter back in AD&D times) is only for 5e, so I will again restrict to just that.
First, different classes can have class & subclass at different amounts, as long as they add up roughly the same at whatever level. If class A has more in base class and class B has more in subclasses, but they are both balanced against each other, that's fine. Again, if we were talking about things like Prestige Classes that every class could take then it would be different.
Second, D&D has
suffered under not having a large enough power budget for races/species. That's why there are NO CENTAURS, just little medium-sized pony people, and the like. This has gotten in the way too many time, it has definitively proven to be insufficient by the limitations of what they can't do. There is no reasoned answer where species doesn't get a generous increase.
Which brings us to Zeroth: power budget AT WHAT LEVEL? Because there's no way to pretend that a species and a 1st level class have the same ratio of power as a species and a 20th level class.
And a lot of this is sensibilities. At 1st level, are you an apprentice, where your species and life-upto-now (background) are the majority of what you know, and you grow into class? Or at 1st level are you a newly minted adventurer, expected to be able to go out on your own, take risks that the common man could not, and not die.
Since people have been doing zero level rules, we can surmise that for some, even weaker than current 1st level could see play. We also know that it's possible to start at a higher level, which will satisfy all of the people who want their character to start off at adventurer level. So one way to satisfy both parties is to have class be a small part of their level 1 power budget, while being a reasonable amount of their level 3 power budget and the majority by their level 5 power budget, increasing from there.
To lay out a framework of how this could look:
1st level
Species: Needs to be able to satisfy large and tiny, flyers, and those innately magical.
Attributes: Part of who you've becomes.
Background: What you've done up to now.
Class: apprentice or lower
I'm not laying out Species vs. Attributes vs. Background, they can be various amount to match what you want, as long as Species contains enough power. But together they would be significantly more than 1st level of a
class.
3rd level
S: Either unchanged or growing, but should be the same across them all.
A: Unchanged (but will get better soon)
B: Unchanged
C: Grown
At 3rd level, Class is now at least pulled even with the least of S, A or B, and is in the neighborhood with the others.
5th (?) level
C: Grown
A: Grown (minor)
S: Either unchanged or growing, but should be the same across them all.
B: Unchanged
At 5th Class could be around the same as the others put together.