This means you will lose quite a lot of HP in one strike. Overall since you often run a Shielder in the team together with the Healer, only the strongest boss attacks will go through the shield and affect the HP of your team. Sadly, while the healing on Basic ATK looks great on paper, as you want your Healers to actually use their Basic ATK a lot, there's one huge issue with it.
It increases the Max HP of the Healer, which translates to increased survivability but also increased Healing (since it's based on their max HP), but on top of that, every time the Healer uses their Basic ATK, all allies will be healed based on their Max HP. Warmth Shortens Cold Nights is a Light Cone belonging to first category. While there are a few Light Cones that are hybrids, majority of them fits into one of the two categories. Support focused - they help the Healer's allies in various ways.