People you cannot judge the power of an energy attack by how much Toho was willing to invest in special effects for it. It is clear and obvious that both of M.Godzilla's red beams are supposed to be more powerfull than his regular blue one. The entire premise of the movie is that Godzilla's energy core is becoming increasingly unstable, growing in uncontrolled, rising output.
Secondly, SpaceGodzilla's carona beam is clearly a very powerfull weapon, just how powerfull it is, and exactly how it operates, is up to fan speculation. Don't use the quality of the special effects as a measure to judge the concept of the weapon.
Now the Corona beam, I am willing to concede that it's directed by S.Godzilla's telepathy. I am not however, persuaded by the level of special effects to dictate the level of power, or the manner in which it operates. When first used on Godzilla, it had a clear, stinging, temporary paralyzing effect. However, after continued exposure to the beam, Godzilla displays a resistance to it's effects.
As we have seen in both previous and subsequent movies, Godzilla builds a resistance to "bolt" attacks. This forms a pattern, which justifies a judgement, that being, that Godzilla's body "learns", and can adapt to certain energy attacks. This however, in no way can be used to judge the objective power level of the Corona beam, it's clear that if it were used against lesser Kaiju, it would result in a devastating, perhaps crippling blow.
Since Destroyah has displayed no such resistance to energy attacks, aside from a higher level of durability appropriate to his character, we have to assume that the Corona beam would strike with the same level of effectivness each time. Suffice to say, The Corona beam used against Destroyah would inflict damage, parhaps at a level equal or slightly lesser than M.Godzilla's red beam.
Destroyah's Micro-Oxygen stream strikes me with more question than answers. What exactly is the composition of such a stream? Being derived from a form of oxygen, does it have a gaseous aspect to it? If so, then would it be able to pass through SpaceGodzilla's shield? What would it's effects be on SpaceGodzilla's mutated DNA? From what we see in the movie, the MOS is a type of "beam" attack, however I think this is more likely the result of Toho's SFX budget, than a proper dipiction of what a Micro-Oxygen projected attack would look like. So we are left to conclude that being a type of "Beam" attack, it would likely be subject to reflection by SpaceGodzilla's shield.
Since the MOS was able to punish an overpowered Godzilla, I am left to conclude that the MOS is more powerful than the Corona beam.
Now we go up close. As we saw repeatedly in the Heisei era, the majority of the fights were at a distance, fought with energy weapons. SpaceGodzilla was especially inclined to fight this way. With an array of abilities at his disposal, it was part of his character build to show how dangerous a monster he was. However he is no slouch going toe-to-toe either. SpaceGodzilla was able to discharge red bolts of energy directly from his shoulder crystals, adding a close-range energy weapon. And we have all seen the effect of his physical strikes, which can conduct a red bolts energy from physical contact.
SpaceGodzilla's endurance is nothing to ignore either, he was able to tank a two sided assault, from both Godzilla and MOGUERA, it was his shoulder crystals that were vulrnerable. Also, when MOGUERA attacked and buried it's nose drill into SpaceGodzilla's shoulder, we see moments later that the wound was healed completely, without scar tissue. His tail also, a very powerfull instrument, able to lift and toss objects far in excess of his own body weight. I suspect this may have been supplicated by telekinesis.
Now the "Gravity Tornado" While I personally dislike the name, I'll work with it. We see no visible signs of it's usage being a drain on SpaceGodzilla's energy reserve, so I chalk it's infrequent usage to the writer trying to progress the story, to mean that they didn't want to keep doing it so they could move along with the plot. With the abilites at his disposal, and the intelligence to use them, I think the writers really undersold the SpaceGodzilla character, and as far as story-telling goes, this could have become a trilogy in itself.
Destroyah up close. Looming over the overpowered Godzilla, and more massive to boot, Destroyah is a Kaiju where only a certain few could stand to go nose-to-nose with. Even Godzilla was beaten back from a tooth and claw fight with the monster, it wasn't until the red beams damaged Destroyah's chest that Godzilla was able to close the gap and inflict injury with his claws. Aside from his imposing stature, Destroyah can use his prehensile tail as an instrument to grab and constrict opponents. The exact nature of what we're seeing when there's an influx of energy when Destroyah's tail is gripping Godzilla, is unknown, so I chalk it up to an all-purpose "energy drain" ability.
Destroyah can also break down into smaller attackers, giving him an entirely new capability of fighting an opponent. Also, as we saw in the movie, after sustaining damage to his chest, when returning to his final form, he had added a "shell" to his chest, protecting the once vulnerable area from the same attack. Which leads me to conclude that should SpaceGodzilla deal enough damage to Destroyah to drive him to break down, should Destroyah resume his final form, he would be healed of all previous injury, and his body adapted to compensate for a previous weakness.
Both of these titans can also fly, adding a completely new dimension to this battle. both can use oral attacks when flying, and destroyah can use his tail for strikes and grasping, which for me, gives him a slight advantage.
Of course I;m not leaving out the famous Katana Horn attack. I think SpaceGodzilla would be able to survive multiple strikes from it, but would suffer heavy injury. Luckily for him, his healing factor would enable him to heal these wounds, but only after given the time to do so, as the injuries would be deep, taking more time to heal than superficial ones.
now for me, there are two X-factors to consider. 1: The effect of the MOS on SpaceGodzilla's mutated DNA, and whether or not this would make the space monster more or less vulnerable to the effects of micro-oxygen. 2: The crystal conduits, and if they would help SpaceGodzilla keep Destroyah at a distance, to sustain a ranged attack strategy, and if they could keep SpaceGodzilla fed at a sufficient rate to withstand Destroyah's own assault.
To me, these two titans are very comparable against each other for different reasons, and a true battle between these two, not hampered by budget restraint and SFX technology would be without question one of the most epic battles the Godzilla mythos could offer. To me this battle could go either way, There would not be a winner of this fight, there would be a survivor.