Unfortunately, in the D&D 5e system, there is no penalty for getting downed and healing is much more effective at bringing someone back from 0 to X HP rather than X to Y HP. You see this "whack-a-mole" situation occurring in PnP 5e mainly with Healing Word since it is only a bonus action, but of course is limited by the amount of spell slots to cast Healing Word.

This situation is dumb in PnP 5e, but Larian's decision to allow the "Help" action to restore a downed ally to positive HP makes it so much worse. It means it is impossible for a party to lose against enemy(s) with a number of attacks less than or equal to half the party size. Larian should fix this, by one or both of:
- having the Help action just stabilize a downed enemy upon a successful medicine check
- by giving downed characters successive penalties each time they go down before a long rest. E.g., gain a level of exhaustion each time you're downed. Once you get 6 levels of exhaustion you die; a short rest restores 1 level; a long rest restores all. Or maybe failed death saving throws persist throughout the day. Something.

Note: I'm not totally sure that Help still brings characters to 1hp, since I refuse to use it in my playthroughs. If it actually only stabilizes PCs (and enemies still focus those downed PCs), then it still should at least require a successful medicine check so that it's not guaranteed.