Rock, Sand Water, and strong thing such as the elephants hipps, gorillas, rhino, and hoofed creaures with thinner legs they can beat Scar if they cooperate, the writer just made Shujaa look the strongest. In real life he'd be tall but Shujaa's not the species you'd consider the strongest.
Kion can beat Scar, but he'd needs ally and friends to help him, this writer just didn't form any of the fights in the realistic scene of an animal's real skills. Cats can outrun the baby gorilla, Jasiri could be leader number two during the war with the real strength her specis has, lions and tigers they're in science like they're two of the strongest cats, the cheetah the fastest so if Fuli helped Kion the sparks wouldn't be hard to put out. More than their real strength this writer hasn't let the cubs learn how they could use stuff in their enviorrment for emergencies, much more of the fire would have been put out if one hurried to the river brought water to the elephants and the two young cats to splash on the dirt in the Kilio Valley fire episode several of the hoofed animals could have helped with a breif trip to the river. Beat Scar for good, they could even learn what would ruin Scar's metal looking thing that seems to magically form flame whether melting it or letting water destroy the ashes on it. That's the solution that would make the solution more eternal.
The writer of the Lion Guard just hasn't quite balanced ease and difficculties in the scens of the two teams against each other.
Kion's also much braver than his father, and Kion is more willing to confess. Kion has the strengths of a real hero he just hasn't been offered the clearest scenes that would make it clear the youngest kids who watch this show. For the safety of both Outlands and Pridelands as you've both said Scar must be defeated.