So, you've bought your tank an additional round of dealing damage. That's not what I'd call wasteful.
However, if my tank is getting whupped, and refuses to move to safety, that's her problem, not mine.
Nope. That damage you healed is gone again. A goblin sneezed and that took out the HP you healed, sorry. They're back to where they were and all the damage came through, your healing was pointless.
On a strict timeline of damage for time, 5E massively values damage over healing.
I refuse to find out what a quick action is. Those were supposed to die with 3e. Also, I'm not sure how healing isn't "actually doing something." If my healer chooses to fight instead of heal, I'd call it "actually doing something else."
We're how many years into 5E with debates over this potion rule, you absolutely have at least heard of this one.
Regardless though, we're talking efficiency. In a strict "The way the numbers go in a fight", dealing damage or preventing your opponent from dealing damage (Though stuns) is most efficent on taking down opponents. Healing's numbers are too low. You're not reversing an entire turn, you're barely reversing half a turn
But...the PC that you just healed did more damage. Does it only count if the healer does the damage?
If my PC dies because my battle plan was to stand right next to the big-bad and swing it out, even when my damage forecasts said that I'd be taking an average amount of damage greater than what my healer could provide, and I told my healer to back off because "I want to die - it's more efficient," and then my GM chops my character's head off because my jerk of a cleric-buddy was waiting behind cover to Healing Word me but lost initiative ( even though we knew the initiative order at the beginning of battle), then I agree. He's a "jerk-ass" and it's all his fault.
And if the healer did damage instead, then the enemy would be dead because 5E doesn't have much healing on either side. Your healing can never out-pace the damage coming through. The only way to lower the damage coming is to murder or shut down your opponent. Running doesn't work.
That big bad is an idiot in your situation then, because he's just wasted his turn to get away from the team who's been firing at him from range the whole time because your party isn't just two people. He's wasted a move that could be used to get into a better position, do some sort of spell to lock down other people, and wasted all of it on a double-tap. He'll be eating an entire turns worth of attacks for sitting around like that and your entire team is going to know you're not playing folks inteligently, you're being a spiteful DM.
Playing Apex, y'know what happens when folks in a firefight decide to focus on the people who are down rather than the ones shooting the oncoming bullets? Those people get killed because they're being dumb. That's the exact playstyle of someone who goes for the double tap in the middle of being actively shot at by the rest of the party