Why didn't he just grab him when he had the chance and burn him from the inside out? He's indeed trash, but I doubt he'll ever become anything since he can't even use the talent like any person with a single functioning braincell would be able to... Just die already you shitty excuse of an MC so we can get one who actually can use their brains for something.
The MC is just an idiot. The moment there was a mention of thermal control, I immediately would've known how to use it "correctly". I mean, increasing and/or decreasing a targets (be it an item or a person) temperature is really powerful and even a little kid would understand how crazy that power is. Just because someone you don't actually know tells you it's useless, what kind of a brain dead moron would actually listen to it? Why didn't he even try out his power to find out it's limits? That's what I would've done, immediately after knowing about it. What is wrong with all these manga MCs that have less than 0 imagination? How the hell have they even managed to think of becoming amazing, when they apparently don't have any imagination whatsoever.