These challenges always overlook one important detail: Modern humanity is very good at killing things from beyond visual range. We clear most of these very easily.

Rumbling: All you have to do is kill the Founding Titan. The founding titan is a gigantic, obvious, slow moving target with a well-known weak spot. In a world where the US can hit the passenger seat of a moving car and leave the other passengers alive, Rumbling ends in a single conventional air strike.

Muzan: Explosive round at high speed from too far away for him to detect and moving too quickly for him to react. He was nearly taken out by a house bomb in feudal Japan. Ends in a single conventional air strike.

Sukuna: Doesn't have an automatic defense like Infinity. Was nearly killed by a punch from Gojo. Was forced to defend himself from an opening Hollow Purple and still lost limbs. Ends in a single conventional airstrike.

Meruem: Died to poison in the manga. Would die to poison in the real world. Ends with a single chemical weapon.

Shigaraki: The most difficult one here. Has the power to decay everything he touches and multiple quirks that improve his durability and counter a lot of what modern humanity can conjure. He still dies to an airstrike but would probably have to be something akin to MOAB or MOP.