So... Here's my take:
Whack-a-Mole gameplay might be the "Most Efficient" for the purposes of spending spell slots... but it's also the absolute worst for any kind of narrative structure. Unfortunately, due to the way healing works in 5e, the average healing spell only restores -about- 1 hit's worth of damage (assuming you roll well), which makes keeping characters up into a full time job for anyone who possesses healing magic.
The answer isn't to remove the whack-a-mole-ability of Healing Word. The answer is to increase the overall function of healing while greater incentivizing keeping player characters upright.
So! Healing Word and Cure Wounds provide their normal amount of healing -and- allow the target to spend hit dice based on the spell slot used as a reaction, allowing a character to gain significantly more hit points than the average attack deals.
But! Failed Death Saving Throws do not reset, and instead persist until the end of your next long rest. So letting someone go down multiple times becomes a serious risk of losing a party member before you get the -chance- to heal them on their 3rd or 4th down of the adventuring day.
Whack-a-Mole gameplay might be the "Most Efficient" for the purposes of spending spell slots... but it's also the absolute worst for any kind of narrative structure. Unfortunately, due to the way healing works in 5e, the average healing spell only restores -about- 1 hit's worth of damage (assuming you roll well), which makes keeping characters up into a full time job for anyone who possesses healing magic.
The answer isn't to remove the whack-a-mole-ability of Healing Word. The answer is to increase the overall function of healing while greater incentivizing keeping player characters upright.
So! Healing Word and Cure Wounds provide their normal amount of healing -and- allow the target to spend hit dice based on the spell slot used as a reaction, allowing a character to gain significantly more hit points than the average attack deals.
But! Failed Death Saving Throws do not reset, and instead persist until the end of your next long rest. So letting someone go down multiple times becomes a serious risk of losing a party member before you get the -chance- to heal them on their 3rd or 4th down of the adventuring day.