Just butting in a bit on the improvisation debate: DM fiat is a problem because anything a DM can fiat, sufficiently well-designed rules can duplicate.

Example: Suppose a player is being "creative". It's a tough fight, and the enemy has lots of hit points. The party is taking too long to kill the creature and running low on resources.

Our "creative" player says "I attack the monster, then twist my sword in the wound, dealing double damage!"

Now maybe you think this is a sufficiently cool description. If you don't, imagine that the player had described it in such a way that you would indeed rule it to be double damage. So you let him get away with it.

Later that fight, or in another fight, the player again decides to deal more damage. Maybe this time he says,

"I attack the monster, then jump up, throwing my weight into the thrust to push further and deal double damage!"

Now the player can just keep doing this. And at some point, if you're a half-decent DM, you're going to say "this time you just deal normal damage". Maybe you only let this sort of thing happen once per fight, or you only let it happen when the fight is especially hard, or you only let him pull this sort of thing off once per session. You put some sort of limit on it.

Great. You've just invented Encounter Powers. Or Daily Powers, or "unlocked when the fight is really hard" powers.

The thing is, you have a number of choices of how often you let the player deal double damage. And whatever frequency you choose, this will affect their average damage. Similar things can be said if the player is instead being "creative" in order to push monsters around tactically, or debuff them, or whatever. Whatever you do, you're faced with the question "what should the player's average damage dealt/damage taken/control of the battlefield" be?

And that question has an answer. Not just an answer for your game, but potentially a set of answers that can cover everyone's game. After all, in the end it's merely a mechanical question of how much damage the player should do to keep the fights functioning as intended. The answer may be hard to discover, but it's harder to discover when improvising on the fly than through rigorous playtesting. A sufficiently competent game designer will come up with objectively better answers to this question than you, and even a mediocre one will come up with better answers than the majority of DMs. Rules will always be better at handling improvisation than fiat, because fiat is created on the fly, while rules, at their best (which is what 5e is supposed to be) are tested.

Um dos acertos do playtest é ter deixado BEM claro que perda de PVs geralmente não significa ferimentos concretos, e sim desgaste físico/psicológico do personagem. Então, um golpe bem sucedido ("acerto" no dado) desgasta mais o alvo, enquanto um golpe não tão bom ("erro" no dado) causa bem pouco efeito - mas ainda assim exige um pouco de esforço pra ser desviado/defendido/etc, removendo alguns PV.

Nego reclamando na Wizard. Que guerreiro causar dano no erro é irreal. É forçar a barra demais.

É estranho tu imaginar que o mesmo pessoal do roliplêi profundo enxerga combate binário: todo golpe TEM que acertar ou errar, não existem defesas, armadura, escudo, 'parry' e etc.