Let's see .. I'm no expert with this kind of thing but im gonna give it a try ..

The only reason i think why 3rd Raikage is Stronger than the 4th Raikage is, because of 3rd's Passive .. 3rd Ay gets more Atk/Nin and Def for each extra chakra you have, so making a team with one chakra feeder can make 3rd Ay a beast .. or even without a chakra feeder ninja, as long as you have extra chakra, he will get extra additional buffs .. Not to mention if you put all high-leveled equipment, runes and magatamas with him and also the buffs from his team like Darui's Barrier and Lightning Main's Passives ..

While on the other hand, 4th Raikage c*so deal massive amount of damage, but and it has a but, but you need to make him powerful enough to deliver great number of damage .. Without proper equipment and items loaded to his arms, this Raikage will fail to win battle ..

When it comes to Standard Attacks and Mystery Skill, 3rd Raikage is the winner again, he can do a Standard Attack that can make damage also to the other ninjas in line and his Mystery Skill can damage all ninjas in the line where his target is .. Unlike 4th Raikage, he's prone to Clone-Decoys, once he tagged a Clone, he will attack it again and possibly start a combo that is useless ..

That's the only thing i can think with your question, let's wait for other users to share their thoughts and opinions about the Raikage Family ..

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(EDIT : Oops! I didn't see the "in the arena" part .. anyways, still close with your question, hope i helped you even a bit)