So, after some more playtime...
The defensive deck feels non-viable against the enemies with escalating damage per round, because it doesn't have enough block (while having slightly too much healing) to compensate for its lack of damage output. A little more damage, a little more block in exchange for some healing, or a few of the + modifiers on a couple of the cards, and it'd feel like it's up there with other decks.
Or you could give it one more lifesteal attack and the first level of the relic that adds block on lifesteal...