If he is always taking Damage, then he will eventually have to do a Rebirth and lose a Shard. The other player would be playing more cards and be able to do more Counter Spells and ManaSurges in the game.
We've put this to the test, and even with losing shards for rebirths, he still always wins due to spells NEVER hitting him. The other player just can't outpace him. I can record a play session with a friend if neccessary, but we tested it thoroughly. He's practically unbeatable in 2 player.