TFT Olaf, not only inmune to CC, but immune to the damage that comes with it

So I know Olaf Ragnaror ability makes him immune to crowd control, but as well it mitigates all the damage from those spells that deal any cc. Last game I lost several rounds as my three stars leblanc and quiyanna, both mages with the 6 mage bonus, 6 ocean bonus, kept spamming spells on a two star olaf with one quarter of HP, dealing nothing, and dying as he healed the little damage they did with basic attacks.

I cannot imagine this is the intended use, as it is not how it works in Summoners rift, and its stupidly broken