In hindsight I kind of prefer it to grinding through go a'la 5E.
By overdoing it I mean using it all the time or using it gotcha style.
Hit the OC wizard the other night with finger if death. Flunked the save and didn't even get KOed. Even if he would have healing word isn't to far away.
They're level 8 now, designed a stinker if a lair to get through CR 17 Dragon, traps, terrain, spells etc.
Just kinda sucks the fun out of the game as DM. There's just not much you can do to challenge them and starting to hate Xanathars (healing spirit, absorb elements etc).
And if thy had dropped and no one had used healing word, then the PC is a zombie and potentially permanently dead. Heck, a DM might rule healing word doesn't work, since they are supposed to become a zombie by the start of the enemies next turn.
I don't know what to tell you, as a DM I've never really felt this. Sure, I have had fights that the players couldn't be challenged on, but I always knew I could pull it off, and even if I knew the players would be fine, they rarely did, and their panicked flailing often made them make silly mistakes that lead to them ending up worse off than they otherwise would.
Sure, players can punch way above their weight class, but that only means you have to adjust expectations.
The HP of the monsters in the book is only the average, maybe these monsters are tougher.
The monsters in the book usually have the lowest quality equipment, let them upgrade, even something as simple as giving a monster that usually uses claws a club helps increase their threat level.
I've always found more I could do to make the enemies a threat, without breaking verisimilitude or going overboard. And, if you've got highly tactical players that keep their cool and never make a misstep, then yeah, you might need to crank things up to keep the challenge on.