Junkrat is a dumbass, he's crazy and brainless. Just an FYI ^^
I’m accepting of peoples headcanons for characters but I hope you’re not just basing his intelligence on his mental state. If you consider what his character has achieved and is capable of, I don’t think its that far fetched to say that Junkrat is extremely cunning and talented. He literally builds all his artillery, survived an apocalypse, can vertically break in and rob any establishment and even has a voice line where he is speaking fluent Mandarin.
Mental Illness =/= Unintelligence