I would say, go with it and see what happens.

Generally speaking, two toons relies more upon independent action then coordination for success.
In 5's, playing 4 or 5 dps toons, you can quickly burst one target down before the other team can react.
That is playing towards the strength of boxing.

Still, win or lose, you'll be earning arena points on two toons.
You might have fun in arena, you might not. If you do, continue with it as far as you can.
You'll also learn what works and what does not, which will make future arena teams that much better.