In a situation where Seto Kaiba chooses to engage in lethal force against the Thornberry's. Despite being in possession of an otherworldly creatures that could devastate any normal human being, there's not a shot in hell that he would win the engagement and there was never any risk of death to begin with for Donnie.

You're probably asking, what do I mean by this? Well, I'm glad you asked. You see, if you study Donnie's physical abilities in depth throughout the history of The Wild Thornberrys, you'll note that he has in the past been able to demonstrate an exorbitant amount of speed and swagger in his sprint, outrunning top apex predators. If you're unaware, as you likely are since this is information I obtained from my uncle, a zoologist, lions are able to move at speeds roughly 50 mph (80kph) for short bursts of time. Now given that we definitely KNOW that Donnie is able to outpace these creatures, we must make the assumption that either he has the ground speed required to make that happen, OR possesses the incredible dexterity needed to avoid the attacks through his deft footwork.

If we assume the former, that means Donnie is capable of traveling roughly 50ft (15.24m) distance that Seto Kaiba traditionally duels from in 0.6821282401 seconds, faster than it traditionally takes Seto Kaiba to even finish INTRODUCING the monster the he is summoning by several orders of magnitude, if that focus is required to finish the summoning, it's clear that Donnie would have MORE than enough time to close the distance and based on his behavior throughout the show, he would perceive the danger of the device on Seto Kaiba's forearm (the duel disk) and would swiftly attempt to remove it. Now you're probably starting to understand my point. that after closing the distance, the fight is already over.