Tovec, stop being a jerk. You just removed the context from my comment, and then pretended I had said something dismissive that didn't have the reasons for my comment. Not cool man. You want to argue about what I say, then quote what I say, and not just a snip of a section out of context like that.
I'm not trying to be a jerk, even if that is what is unintentionally being perceived.
As far as removing context goes - I cut your comments down for a few reasons. The first is to not turn these replies into monstrously long ones (as you yourself have noted and objected to). The second is to reply to the specific sentence or comment that I actually am replying to. Third, you did it first. You cut my replies down to one sentences as well - and then criticized things that I actually didn't say.
Finally, the wonderful benefit for forums is that people can go back and look at the full arguments made - with a handy button to go look up the full description of what we both said if something was taken out of context.
I am not dismissing it, I am saying I never claimed it is identical, just similar. Again, you first claimed I never said it was identical, and then the very next sentence talked about how it was not the same. You realize the definition of identical is the same, right? I am waiting for you to explain why the difference you note is meaningful for this discussion?
I think you misunderstand what I'm saying when I said "you dismissed it." You did not prove JRR wrong, and when I pointed that out you replied that you didn't try to prove him wrong, that you merely say he is wrong (because he is wrong apparently). That is what I found dismissive - an issue that you seem to address in others that I merely noticed you doing.
Now, do you know what 'similar' means? It means 'having a resemblance in appearance, character, or quantity, without being identical.'
So, when you give an example I look up the qualities that 'have resemblance in appearance' without making it identical. Namely what qualities are the same, but not that those things are identical things. But mostly, if you object to the word itself, then I think you miss the context of what I am saying.
WHAT reasons? All you are saying is they are not the same...not why the differences are meaningful for this discussion.
I am saying the examples you have given, magical fireball and alchemical fire, have qualities - namely explosion and splash - which are important to why we find this ability different from that of a mundane sword swing by a fighter. I cite qualities of limited resources, which you also find inconsequential. I find it difficult to give you such qualities that you seek when you simply say that the qualities I'm giving you are inconsequential.
None of that is inherently a problem. I don't know about "not work as described" as I don't know what you mean by that. But for the others, you seem to think the problem with those things is self-evident. They are not. You're skipping the most crucial step to your argument - why those things are meaningful. I've explained why an ability that does not miss, even on a 1, was present in 3e and nobody had a problem with it (with at least three types of things: 1) spells, 2) traps, 3) mundane splash attacks). There is nothing inherently bad about modeling a splash effect with a melee weapon, and in fact I think that is a good thing to add to the game. And there is nothing inherently bad about it working every round (you can also throw a splash weapon every round, for example - they are very cheap or even free, depending on the character and feats or classes they take).
I wasn't addressing spells or traps. I was merely replying to you why I think people have no problems with splash weapons (alchemists fire) and that such reasons aren't what you seem to think they are.
Also, how can you get them free? I'm intrigued? You can PM me as I'm more curious for character creation reasons as opposed to disagreeing if you could do it.
As for the splash weapons, I disagree. They no more require an attack roll than this 5e fighter ability we're discussing (it also requires an attack roll).
I have to break this up. They do require an attack roll. They can miss. At ranges further than 5 feet they require a roll and are likely to miss, and certainly do not ALWAYS hit (especially on a roll of 1).
And as already pointed out, if they are at the 5 foot range then it hits the fighter/thrower as well. A level of damage that the GWF does not ever try to account for, even though he supposedly "strains" the enemy.
And it is no more limited use than this fighter ability (both are inexpensive weapons you buy with gold - anyone can afford oil or alchemist fire, particularly as you increase levels, and some classes could even make those splash weapons as an ability).
One is a single (relatively minor) investment. The other is a continual investment and can be limited by the number you have on you at any given time. Even if they are free to make, thy would presumably require time to craft. As such you can only do it so many times in a row before you run out. The only limit the fighter has apparently is HP.
And both do damage on a miss. It's a fair analogy to be making.
But again, the definition of HOW they do damage on a miss is not the same. One is an explosion of damage that harms everyone, the enemy, friends the thrower themself if they are in the range. The other is a swing of a sword that can never fail to harm the enemy, and only the enemy.
Why would it have to take up a 5x5x5 square to be satisfactory (you want it to be MORE powerful?) and what other issues does it fail to address? Again, you seem to think we can all read your mind and figure out what you're thinking or something.
You ask why it is acceptable. I give that is acceptable in the game's fiction because it is modeling an explosion which is impossible to escape. Or a splash that causes secondary damage to the squares around it, also impossible to escape. Both of which create a 5x5x5 effect that engulfs the full square the enemy is standing in.
Then you wonder why I have a problem with a fighter ability, which is not an explosion, yet somehow has an effect that is only replicated via explosions. I submit that it would be the same problem I would have if the fighter's ability caused 3 points of fire damage - it isn't a fire effect it shouldn't do that damage. It isn't an explosion it shouldn't ALWAYS HIT everything in the square.
You raise concerns over balance. I don't. I think it breaks the believability of the game. The only way I would find it palatable is by adding many different restrictions and modifications to the ability. And honestly with the amount of changes that need to be made they should either DO those changes, or give up on the ability.