SS4 is a superior form to the god forms. @ me.
All nonsense scaling bullshit aside, the function of it is different and better.
God Ki essentially pressurizes and condenses your ki, and encapsulates it, so that it doesn't leak out. The pressurization adds a boost in itself, and the recycling makes sure every ounce is either used or reshelved. But the stamina drain is pronounced, and it kind of has a set multiplicand. Goku overcomes this using his kaio-ken, and vegeta [uses perfected blue].
SS4 Can still leak energy, but it is a metamorphosis, not a doping transformation. The super saiyan 4 at rest does not spend any ki or anything. The body itself is simply evolved to it's highest potential.
As far as powering up, it has the battle aura of a regular super saiyan, which is to say even though it is an Oozaru transformation, it has access to all of the saiyan's energy being a limit breaker.
SS4 then is closer to Gohan's ultimate form. It gives them ultimate flexibility in how much power they want to draw out, and they can control the rate.
The thing in which they differ is that SS4 is a refinement of saiyan biology, and because of that the Zenkais are maximized. That is why their growth is so insane. Every time they fight, their base essentially climbs up to where their last transformation into ss4 is.
SS4 makes zenkai exponential. the boost is current power level to the 1st' power = new base.
That is why goku in GT keeps defeating people in base after turning into super saiyan 4.
It happens consistently.
Jiren already showed us that god ki isn't actually necessary, but was a boost when goku and vegeta were unsure of where to go from their current states.