In the beginning of chapter 165, Garou is stated to have been given
full knowledge of all forces and energies in the universe. And this isn't some character's dialogue or internal thoughts saying this, it is the
narrative itself stating it. Regardless, it is proven immediately afterwards, as he
replicates nuclear fission to produce nuclear explosions.
Nuclear fission being one of the sole forces keeping our universe together.
After this, he says he feels as if he can
do anything, and then produces the very feat we are talking about through
this sequence of panels. He creates a black hole, and from it, giant beams of energy blasts out from each side, completing the attack.
Based on this context alone, many people have claimed it should be scaled directly to the strength of a Gamma Ray Burst. After all, Garou has full knowledge of how these explosions function, and the narrative straight up says what his attack is mimicking.
Thus, his attack potency should scale to the value mentioned earlier,
10^44 Joules or 1 Foe,
High 4-C.
But wait, there is more to go over here. Many bring up valid arguments as to why this shouldn't be scaled.
Of these, the most notable one is that the attack is FAR smaller than a real Gamma Ray Burst, and thus can't be scaled to a real one, which are far bigger. This is true. GRBs are massive, expanding explosions that reach dozens to hundreds of kilometers in diameter. And looking back at Garou's, it becomes apparent that his is no where near the size of a real GRB.
However, while the attack is smaller, there is no reason to believe that it doesn't have the same quality and function of a real Gamma Ray Bursts. The narrative says exactly what it is, and Murata draws it as a somewhat accurate depiction of what these things actually look like. So in theory, we can simply scale Garou's GRB energy output proportionally in size to an average one. For example, if it was half the size, it would have half the energy. Unfortunately, since GRBs vary in size so much, we were unable to find a good source on how big these things are on average.
Though, Garou did manage to create a black hole, which can be measured for GBE based on size alone. And that is where the low end, compromised attack potency comes in. Therefir has already calculated how much energy would be required to create a black hole the size of Garou's. It comes out to a lower, but still insane
247 Yottatons of TnT (
5-A).
This isn't to dismiss the fact that many do still believe he should scale to the real value. One of the most valid points brought up is the fact mentioned before: Garou has full knowledge on how these phenomena function, thus there is no reason to assume he would create a far weaker version of it.
To an extent, I agree, so I bring up a compromise for both ends.