To be completely honest PCs are so absurdly durable & overmatch monsters to such a degree that they make the average isekai protagonist look a bit fragile. The fact that even a single instance of wackamole healing let alone five or ten is possible without even the slightest opportunity cost is a serious problem. The system being designed to make a moral hazard like wackamole healing the optimal choice by nullifying all of the damage beyond zero only serves to exacerbate the problem.
No, I don't agree. I think it's extremely easy to occasionally arrive at whack-a-mole by error on the part of the PCs or the DM, or -- probably most likely -- though accident thanks to the fact that the dice are really high variance in D&D. And I think that the high variance of the dice means that it's impossible for the designers to avoid the problem unless they so overload everyone with HP and so control hit rates so that they're always in a narrow range -- that is, what 4e did, which turned into a huge slog -- then you're just naturally going to have encounters every so often where stuff goes pear-shaped for reasons outside the designer planning and outside the intentions of anyone at the table.
Further, it's "difficult" to kill the PCs in as much as it takes one attack to down a PC, and two more attacks to kill a PC outright. It's at least moderately common that that can happen in most encounters. If you just never have NPCs with three attacks, or never have NPCs with two attacks and a friend, ok sure. I guess that's difficult if your initiative is accidentally incorrect.
Additionally, healing magic is terrible. Pretty straightforward terrible. First level spells do about 3d8 damage plus 1d8 per level above 1 at range. Healing spells do 1d8+ability damage -- so basically
2d8 -- plus 1d8 per level above 1 at touch (or half that for a bonus action at range). So you just lose a die. And attack spells can do that while hitting multiple targets at no loss of damage. Healing spells? No, your multi-target spells lose
even more dice. Healing is a losing proposition in almost every case. That's why you get whack-a-mole. Because healing
can't keep up
.
This misalignment often gets defended with some vague gestures towards "big damn heroes" or "heroic fantasy" to invoke some kind of isekai/wuxia/etc analog for PCs but in all of those the overpowered main character is generally
capable of having an
oh crap moment where they realize
this is gonna suck but the rules & mechanics are designed so that such a moment can only occur after the avalanche of a
curb stomp battle has been set in motion to play out more like
rocks fall everyone dies with the serial numbers scratched off.
If you don't like heroic fantasy tropes, that's fine, but it's hard to argue that heroic fantasy is not a big part of D&D. No, it's not 20th century D&D, or OSR, but... there's kind of a reason that that style of gameplay hasn't really been featured in over 20 years. Lots of people don't want gritty realism. Lots of people don't want sword & sorcery. Lots of people don't want dark fantasy. Not when they're running D&D. I do think 5e tries to straddle both gritty realism/OSR and heroic fantasy. I also think it's done a terrible job with both of them. It's trying to be the everything game, and I don't think it succeeds at anything but being inoffensive.
However, as boring as the published 5e modules have been overall, none of them have been gritty realism or OSR. Quite the opposite. Most of them involve some plot to save the world, not some scheme to line their pockets. Like it's year 10 and they're just now releasing a book of heists. Indeed, as time has gone on, the modules have steadily
eliminated player rewards from them -- both monetary and magical. I'm willing to bet, sight unseen, the heist book has underwhelming rewards. (I wouldn't be surprised if half of them don't even have tangible rewards.) But... heroic fantasy doesn't care about tangible rewards. It cares about advancing the plot. So I think the adventures being sold have been heroic fantasy. That's what people are buying and playing. They're not kicking in the door to steal the treasure. They're kicking in the door to rescue the princess.