I feel like T1 is a major mana/heal check if you use the traditional dual-tank method that we use. After the split I can keep the tank up using regen + cure 1 at the beginning, but as the stacks start to rebuild I have to switch to divine seal regen and cure 2 to make sure they don't go down. At that point mana is a serious concern if you haven't timed your SoS well.
Here's a good example of why the gear is more necessary than the skill: at the initial pull of Caduceus, he slams the tank so hard you commonly see his health drop to 20% in the first few seconds. Too many times I've seen healers pull aggro because they attempt to overcome this by spamming Cure 2 at the start; 95% of the time we have to wipe it unless the tank can quickly reacquire aggro. For this starting phase, you need to be able to keep the tank up with a single low-level heal until after 5s or so when they've established enough aggro for you to use more powerful heals.