It was an open question, not solely one for game designers. So thank you for the answer.
However, at least in 3e kobolds had 4 HP. Which would immediately render the reaper ability a non-KO ability at least on the first swing. They clearly didn't just have 2 HP as a carryover, as in 4e they had 1 HP (as a minion) and in 3e they had 4 HP. Oh, a non-minion (at level 1) had 27 HP so rather a little more than 2 I would say.
3e raised HPs across the board, for the very reasons you've been outlining (then again 3e allowed power attack and cleave at level 1 so a 3e fighter could kill 2 of these buggers which can't, as of yet, happen in 5e)
in 4e the basic kobold was a 1hp minion - so translates almost exactly here. the 27 HP ones were, I believe Dragonshields, which have 15 HPs in the current playtest (and are definitely not the "standard" kobolds)
The problem is that their ONLY solution is to cut the themes. I am told the cut the themes if I don't like an aspect of a single theme. I am told to cut the themes if I want an old school play. This solution only serves to handicap my players, nothing more. It doesn't solve the issue of kobolds having 2 HP and being able to be defeated by a strong breeze.
Modularity may fix the problem, but I am not alone in thinking that modularity needs to be built at the beginning not tacked on at the end. Beyond that, modularity doesn't solve this problem. Giving me other tools to use is what modularity fixes. Modularity will allow me to not have to use the reaper ability, or allow me to replace the Healer theme. It doesn't change the HP structure of all creatures in the game. Even if a new HP system is introduced, such as one relating to wound points or similar, the issue will still exist because it is expected that you convert the existing material over to the "WP" system, so what is silly in one system will remain silly in another.
Modularity is a toolbox, it isn't a cure.
It's the initial playtest - no way they can be expected to have all the answers.
But you central complaint really just seems to be that 2 HP kobolds have too few HPs and are too weak. Really easy fix: have kobolds have 1HD-2 (to simulate weakness) min 2, instead of a static 2 HPs. I'll be surprised if the actual rules don't have this exact rule (it's the way 3e did it, assign an "average" HP to a monster but supply the math behind it so you can easily generate your own number.
A. It impacts more than just creatures with less than 3 HP. It works on everyone, regardless of HP. It only insta-kills people with 3 or less.
B. It insta-kills people with 3 or less HP. ON A MISS.
C. At least magic missile says it can't miss. The reaper ability says no such thing. Ergo, the MM ability has a REASON it works that way, the reaper ability does not.
D. Yes "it is magic" is a viable defense for such things.
E. I dislike MM too, in case you are wondering, for the exact same reason. (In my potential 5e games I would make it a 1st or maybe even 2nd level spell. Something that costs something to cast, instead of free 24/7. But this isn't about MM.)
You keep saying "on a miss," for this to make any headway here you have to move past the "miss" part and just accept that it's damage dealt when a certain condition is met. Think of it as anyone who has this training
never misses, maybe that's too much - but it's got some precedent (Bulls Eye, Green Arrow etc.)
I despise the "it's magic" explanation. I can just as easily say the reaper ability is "mythic" (and you know what, there's not enough mythic stuff in today's D&D - which is a loss.) the training as mythic appeals to me.
The mage gets magic missile, which represents the mage's innate ability to conjur "force" to leap from their finger tips and strike an opponent. It does not miss and has a set effect. It does 1d4+1, not the mages attack stat. On average the missile is doing less than the fighter too. Also, it has an explanation, limitations, can be countered and is codified. On the other hand, the reaper ability is none of these things. It can't be countered as long as the fighter could hit but misses. It does MORE damage (on average) than the missile and it does it to all targets, so long as he misses.
Magic missile scales better and quicker than reaper (mage gets more missles faster than the fighter gets a bonus to his strength). Further, the fighter will never intentionally miss as his minimum damage on a hit is 9 and average damage is 14. Further low damage resistance is a pretty common thing, and I bet they bring it into 5e, meaning the ability would be countered in certain circumstances.
For everyone else, except the slayer, a miss is a miss. The slayer misses but the kobold still dies. I don't need real world explanations for that to see it is a flaw.
No, it's an intentional feature of the Slayer theme. One you don't like, but it's clearly an intended feature.
We have at least 2 instances (magic missile and the slayer theme) of at will damage with no roll, clearly they're testing out a possible feature.
I can't fault them for being all "troll" to see what we react to. But I honestly doubt they are just doing it to see if people react. I think they see the mechanics as legitimate offerings or things they want to test. That is why, as I said; If there IS a good reason why the fighter can always, reliably do 3 damage to every creature on a miss then let [us] see it.
The problem is, there are plenty of reasons; I've even listed several which I think
are good reasons. You just disagree as to them being good.
What I have said is that 2 HP is too low. That no one should not be able to kill them on min damage. That the slayer does it WITHOUT HITTING at all.
I have said kobolds SHOULD BE WEAK. I don't know how often I have to keep saying that. They should be. I think that the playtest makes them TOO DAMNED WEAK. So weak in fact that they offer almost no contest to a part of LEVEL ONES. If the enemy isn't threatening at level one then they are never going to be threatening. I see over and over that kobolds aren't threatening enough in large groups, which is when they should be.
And I think a level one ability that allows you to drop certain weak creatures, 1 at a time, even at first level, is fine.
Let me ask, have you
played through this encounter? Because you keep saying, too weak even in large groups. When more than just me has stated, they are actually a decent threat in large groups! The fact that no character died, does not mean they were not a significant threat!
