So this is something that has been on my mind and I have brought it up a few times in the chapter discussion thread:
In that chapter it seems like the point is made that for shoto to use 100% of his fire he needs to basically raise his temperature to his utmost limit. But... doesn't that mean that to some extent both halves of his quirks at sort of at odds with one another? at least when it comes to using his fire side's full power at least. Shoto's ice basically helps him lower his temperature and thus reduce the damage from his fire. And his fire can potentially do the same for his ice.
But... in doing that then doesn't that mean each side of his quirk basically also limits the other? As in, if shoto uses his ice to reduce his temperature then he is also lowering his fire output since the fire requires heat. And the same could potentially apply to his ice.
now, that isn't to say shoto's quirk has a bad combination but there are so caveats to consider, perhaps some that shoto has not even discovered yet. The most important consideration is that if shoto aims for full power of one side then the other one is basically shut down. And in activating the other half he is lowering the one he was already using. Of course, we know there is a point at which both are usable but by all appearances shoto shouldn't be able to use 100% of either at that point.
I am thinking that perhaps in the future shoto will aim to vastly improve the speed at which he can go from zero to full speed between sides. Which will allow him to maintain his body temperature within safe thresholds and maintain his offensive power. Well, that or perhaps shoto eventually figures out how to have 100% output with both sides at the same time, which is the absolute best case scenario for him. But that doesn't seem probable for the time being, at least with the apparent current dynamic.
That also brings me to another point... perhaps endeavor miscalculated what the best quirk to mix with his own would be. Hot and cold has its merits of course but 100% output being limited by the harm it causes to the body or by the other half being used is just short of ideal. Perhaps the ideal quirk to combine with his own would have been one that effectively makes the user heatproof. Something like tetsu's or kirishima's quirk sounds pretty much ideal for instance (though I am not sure of kirishima's ability to handle heat). Being heatproof would basically mean the user could abuse fire without consequence to his own body and push the quirk well further and for longer.