Yea, SSG is colossally stronger than their regular base forms. But their base forms have had the SSG God power imprinted into them. Goku literally stated that his power had a ridiculous increase because he'd adapted to the power and he still had comparable power to SSG as a Super Saiyan, meaning his base state increased by the proportionate amount of the SSG. And we don't know how Vegeta got the SSG, either. For all we know, its when he achieved the SSG form on his own that his own base power increased exponentially. The point is that from what's seen, the SSG transformation drastically increases the user's power when it's first awakened due to its divine nature, allowing the user to increase that power, but doesn't expressly give the user the same ridiculous multiplier later, rather just a significant boost in power instead. Your multiplier is not accepted by the vs battle, either, so this trillions of times stronger transformation should not be the standard for the rest of the Saiyans.
Just because the saiyans absorbed God into Base doesn't necessarily mean that the transformation itself becomes less powerful. That is never stated nor implied anywhere else in the series.
You mentioned yourself that "the SSJG transformation drastically increases the user's power when it's first awakened due to its divine nature, allowing the user to increase that power, but doesn't expressly give the user the same ridiculous multiplier later, rather just a significant boost in power instead"
Read what you're saying
How can you even attempt to prove that the transformation lost efficacy when you yourself admit that every single time the transformation is used, the user gains a "significant boost in power"? For all we know that "significant boost in power" is literally just the same multiplier we got from the original SSJG transformation since the show doesn't retcon that at all.
VS Battles are the same group of goons who say that
1. SSGSS magically made the saiyans 2C while their base forms are 3A after the ToP even though before the ToP they remained 3A with the transformation and they still use the exact same transformation. Why does the exact same transformation suddenly allow Goku and Vegeta to skip tiers?
2. SSGSS is 2C while SSJG is 3A, even though SSGSS is accepted as SSJG and SSJ combined, and SSJ is accepted to be a x50 multiplier on the wiki
3. Base Gohan in Super Hero is 3A while SSJ Gohan is 2C, even though SSJ is accepted to be x50 Base on this god damn wiki
The people who disagree with the scaling for SSJG make far too many nonsensical claims for me to take their claims seriously
And let's say that we ignore the "trillions of times stronger" part of my own argument. I'll be nice and admit that I'm wrong for this upcoming example
Broly was able to outgrow the likes of SSJ Vegeta after clashing with him a few times, despite starting out weaker and less skilled initially. With Wrathful, a transformation that mirrors Great Ape, he was able to clobber both Super Saiyan God Vegeta and Super Saiyan God Goku, and kept up with Goku even after he went into Super Saiyan God Super Saiyan
At the barest minimum, Broly would have gotten x50 stronger by simply outgrowing SSJ Vegeta
He also vastly surpassed the godly duo with a vastly inferior transformation, which would increase his power by at the bare minimum, another 50 times, assuming you lowball Super Saiyan God to only x50 stronger than Super Saiyan
This means, with an EXTREME lowball, Broly got x2500 stronger in a matter of minutes
Any advantage the Gammas might have on Broly will just evaporate entirely after fighting Broly for a few minutes, and since they don't go for the kill in character (before you argue this, Gamma 1 didn't try killing SSJ Gohan despite being far stronger, and Gamma 2 was too stupid to realize Piccolo escaped his blast), they would just get outplayed. Broly also counters their adaptability with his own.
The only argument that I can see for the Gammas winning is if one or both of them blow themselves up, but we don't know if Broly can outgrow them enough to tank the blasts, and if the latter ends up happening, then all 3 die.