I refuse the argument "you need to remain weak, little rogue, so us others can have enough combat time".
The rogue isn't "as good as the others", you yourself said it. But there is nothing the Rogue can do out of combat that is qualitatively better than what a Druid or Warlock or Bard can do out of combat. They don't do the same things (at least not in the same way), but they can all pick ooc tasks and be successful at them.
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So I ask again - why single out the Rogue as the sole class with no or little build flexibility to contribute in combat especially given its class description which suggests it should be excellent in combat (fearsome assassin, etc) ?
Again, if you want to be able to murderize your foes, why play a rogue when a fighter (or sorcerer) is much better at the job, which isn't just "killing the mark quickly" but also "...with as little risk of dropping yourself as possible"?!?
And again, those of you answering "I don't mind my rogue being weakish in combat, he's excellent out of it" - you are not answering the core question!!
If you don't mind its combat capability then you won't mind if we boost that? Right?
And don't come running with "if you boost combat, you need to take away from out-of-combat, and I'm not having that" - I am not taking away anything from you. If the player chooses a combat focus, it is not a problem that this becomes the focus - it is the answer.
And if you answer that with "but I need my rogue to be a weak combatant" I'm saying "but I'm not removing the possibility to build such a rogue, I just want to add a combat build".
Only if you answer that with "but I need Rogues to be the only class that isn't and can't be built for combat, despite being a martial class clearly advertised for precise strikes" are we done, because then you are clearly unreasonable.
So what it is? Where do y'all stand?
OK, I'll start with the last question. You know where I stand, I think the rogue plays just fine as it is.
And I will also state that this thread is like many others where there is a declared "problem" with the game, with the assumption that it's a problem for everybody. So when you ask for input with that approach, you'll often get a debate about whether your declaration is right or not, instead of just input about how to tweak the rules.
I don't think "it's not as good as the others" and I personally don't care whether there is balance between the classes in and out of combat. However, in my experience when I've played in games where people focus on things like DPR, they also tend to focus on spotlighting, balance between the characters, etc. So making a rogue more deadly in combat can affect how players who care about such things feel about the rogue in relation to other classes.
We don't look at "who is better at the job." The PCs are the PCs, they are people in a world that have banded together for some reason to go adventuring. If a combat ensues, their only real concern is surviving it. If the rogue takes 4 rounds to kill their orc, and the fighter only took 3, they don't care. All they care about is that the orcs are dead. The fighter might have had a round to go help the wizard with their orc, or whatever.
Our characters aren't designed to "murderize their foes," and when they are in combat, they aren't in a competition to see who does it "best." That's not their focus. In addition, they expect that a fighter will be better than a rogue in combat, and that magic is often more powerful than mundane combat. If I was to complain about anything (and I have) it's that there are far too many spellcasting classes, and they get spellcasting at too early a level.
I haven't seen rogues dying more frequently than other classes, nor have I seen any significant difference between classes in how quickly they defeat their foes in actual gameplay. Combat is dependent on a lot of variables, and with the rogue's mobility and, as they get to higher levels, their defensive benefits make them a considerable asset in any combat. Combat is generally a team effort in our play, so it's more about each character contributing, rather than keeping track of individual kills.
All of this comes together to a very simple conclusion. The rogue is just fine as is. For us. It meets all of our expectations in and out of combat, and considering altering the combat capability of the rogue alters the game in ways we don't want. In particular, we prefer a grittier, "normal people" doing heroic things to "heroic people" doing super-heroic things. So if anything, our approach would be to reduce damage output across the board, and if that means lowering the rogue less, that would probably be OK.
If you feel differently, then go ahead and make changes. And if nobody at your table minds boosting the rogue's combat without altering anything else in the game, then you're good. But saying that there is no need to consider the effects of balance across the entire game and all classes if you boost the rogue's combat ability can cause problems in other people's games. Because some people may like the overall balance of the classes, and boosting the abilities for only one class alters that balance. Just because you don't consider the out-of-combat abilities worthy of consideration doesn't mean that others don't.
The rogue is designed as a skirmisher. To get in, make a (big) hit, and get out of the way of danger. They can benefit from their increased damage output using ranged or melee weapons. They can help turn the tide of combat more than just about any other class with these abilities, by providing that extra damage (either before or after their ally) that pushes the total damage in that round over the threshold to drop the creature.
Beyond that, we don't really think in terms of "alpha strikes" "burst capability" or "going nova." It's just not our playstyle, so I can't really help with those. It seems to me that Dual Wielder, Martial Adept, Sharpshooter, Skulker, and Sentinel all benefit the Rogue greatly in combat. Additional archetypes that have been published provide other ways to gain Sneak Attack as well.
Beyond that, if I were to consider altering the Sneak Attack mechanism, I might look back to earlier editions that multiplied damage instead of adding damage. This can be much more variable (not just because of the die rolls, but the die types used, etc.). Perhaps the Proficiency bonus could be used as the multiplier (x2 at 1st level, x3 at 5th level, etc.) I have no idea how the math scales out, and the damage increase happens slower. But it might address the issue that you have.