What I was saying is ambiguous is just how big of a gap there is between Deryl's weapons and Xanthe's (if any).
We haven't exactly seen the limit of Xanthe's weapons in terms of how much damage they can do, but we do know that they're effective against B-Class monster and "useless" against A-Class monsters, but what does he mean by useless?
Useless in the sense that there's no point giving them to normal humans because they'd easily get annihilated without a way to protect themselves?
Would Xanthe's weapons, in the hands of MC or Deryl with his mech suit become effective?
Again, I wouldn't say Deryl's weapons were that effective against Cole. If you gave his weapons, even with limitless power, to a group of humans, they would almost certainly die to Cole.
They were a good way of depleting Cole's power, but that strategy still heavily depended on Deryl and MC's maneuverability and almost failed.
And then there's A-Class monsters having significantly tougher bodies than a level 4 superhuman. So what effect would Deryl's weapons have on them? Would Deryl and MC be able to replicate the strategy they used against Cole on a typical A-Class monster?
Perhaps we can try to analyze the parallels between Cole and the Asura.
This is my interpretation:
1. The strategy against Cole exploited his capacity to heat up his body and melt the projectiles. Cole can output up to X power at a time, so if you shoot him with so many projectiles that he needs more than X power to sustain enough heat to melt them, he will start losing heat to the point that the projectiles won't melt and start harming him.
2. The strategy against Asura was to repeatedly attack the wound till penetration. MC focused the majority of his attacks to this wound and after 3 hours, not only he penetrated his internals, but made it through the other side. This result makes it highly likely that the reason it's skin was so tough to break in the first place, was due to Asura's high internal power. After 3 hours of getting hit in it's weak points, it's internal power was almost spent and MC was able to break through both the wound and the outer skin. Since MC's damage is mostly mechanical, even at low internal power, his attacks are still strong because the velocity of each attack and the material used remains mostly the same.
This generally aligns with my idea of Xanthe's weapons being low on power. If you can get a million of these weapons shooting simultaneously, then you probably have enough power to kill even an A Class, but not only the logistics are impossible, but chances are there don't even exist enough weapons to reach critical mass.
Additionally we know that nukes can actually deal with monsters. The problem is that they aren't efficient. If all it takes to kill the Himavat is a few hundreds of nukes, then humanity can technically kill these monsters. The problem is that after that they will face extinction from the fallout and nuclear winter.
So to summarize my idea:
The general body toughness that stronger monsters have is a function of
1. Monster line. Physical lines have stronger bodies.
2. Internal Energy. Energy adds toughness to the body till it gets depleted.
3. Unique defensive mechanisms. This adds an extra layer of defense that makes some attacks more or less effective than others (like for example, Cole would be immune to heat based attacks).
Something like the Asura doesn't have unique defensive mechanisms so any type of attack can potentially kill it, but at full power it's body is so strong that you will have to hit it repeatedly with high impact weapons to decrease it's internal power enough before the attacks manage to break it's skin.
Xanthe's weapons can potentially harm even an Asura assuming that there exist enough of them, but the logistics of attacking it that way are impossible because each weapon has a weak power core.
Deryl's weapons also can potentially harm even the Asura and he will have an easier time because his power core holds significantly more energy and his unique power allows his to create bigger and stronger weapons that deal more damage per unit of power expended.
Essentially I think you are correct thinking that humans will die before they kill the monster. What I'm suggesting is that even if the humans can survive, without better designs like Deryl's and better batteries, even all the manufactured weapons won't be enough.
Regarding Xanthe's weapons effectiveness if Deryl was using them, they would be significantly stronger because he would use his Philosopher Stone to power them instead of whatever energy core these weapons come with. If he was just using the default energy core, chances are that they would be useless.
