Just to echo and expand on what Tobei said: it is hard to judge ninjas being used in arena, because arena makes it so the playing field is relatively even. For example, ninjas that produce clones and additional bodies are stronger in arena because those bodies are harder to kill, i.e. Kabuto. Where as ninjas that require being stacked to be relevant, i.e. Edo Hiruzen, don't shine as much in arena.

I always viewed arena as assessing the strength of the ninja formation more than the strength of an individual ninja.