As others have said, this will lead to a general problem against bounded accuracy.
That is a fair question. If expertise creates a problem against bounded accuracy, is it ok for the rogue or bard to have it?
Blessings of Knowledge has the important constraint that it only applies expertise to Arcana, History, Nature or Religion. Those don't impinge on the core skills for Rogue.
Indeed. Nor does a general granting of access to expertise. The rogue's core skills are only impinged on if a player wants his character to be roguish. Even so, rogues have other class features that make them superior in these skills, even if others share expertise.
]QUOTE]Thieves Cant is a ribbon.[/QUOTE]
Yes. It is a language, and so I give it one point from Trained.
Sneak Attack is reasonable, but doesn't compete with Fighters once they have their Extra Attacks, bonus action attacks (from various sources), and possible reaction attacks (e.g. Riposte). It isn't correct that Rogue out-damages Fighter.
Notice that my break down includes Extra Attack and shows Sneak Attack to be stronger at level 6.
6th Rogue with Rapier, Studded Leather, 18 Dex (ASI), AC 16
6th Fighter with Rapier and Shield, Breastplate, 16 Dex, AC 18, Shield Master
Rogue almost always one attack at +7, d8+4+3d6 = 8-30
Fighter two attacks at +6 (with advantage, opponent is prone), d8+5 (dueling) + 2d8+5 (superiority die) = 13-34
Expected AC 15, Rogue hits 0.65, Fighter hits 0.84 (advantage). Rogue expects about 12 damage, Fighter expects about 20. Shield Master is strong, but Fighter could be exploiting PAM or GWM and doing more than 20. And Fighter can at some point use Action Surge to spike their damage much higher (in practice Action Surge beats out Assassinate).
Your analysis includes specific archetype features rather than looking at base classes. Yes, certain archetypes are more damaging than others, but the others have other benefits. When comparing classes as a whole, we should reasonably assume that the archetypes are roughly balanced having features that offset each other through various parts of gameplay.
As to advantage, the rogue can easily hide and gain advantage through that.
Uncanny Dodge is beneficial. Foe has an expected +5 or +6 to hit. Rogue is hit about 0.5 of the time. Fighter is hit about 0.4 of the time. Most foes are multi-attacking at 6th level. So Rogue mitigates one to 0.25 but not the other. In practice, Cunning Action for Dash or Disengage is the Rogues' greatest ally.
Also note that a stealthy fighter would have disadvantage from heavy armor, but with a shield would probably have an AC of 17 or 18. If the rogue took +2 Dex at 4th, he should have an AC of 16. (Studded leather is inexpensive.)
Even with your analysis, optimizing your fighter, he is only out-damaging the rogue by 4 out of 30.
Even more importantly, we are comparing fighter to rogue under the assertion that the fighter is outshining the rogue at roguish things. This implies that there is both a rogue and a fighter in the party. If there were only one, why would we care? But if both are present, then (depending on initiative order) your rogue would
also gain advantage from his opponent being prone by Shield Master. The Fighter and the Rogue
work as a team, not as adversaries.
Meanwhile, the rogue is still dominating checks, with a minimum roll of 10 on every check. The rogue is still the stealthiest and sneakiest, though maybe he has a teammate who can almost keep up. Now instead of scouting ahead of the party all alone, the rogue has a partner. When the partner fighter/ranger/whoever gets found out, the enemy says, "Ha! I knew there was a rogue in here!" Meanwhile, the even more stealthy real rogue stabs him in the back. Go rogues!
The analysis omits multi-attack
No, I included Extra Attack.
and the superiority of the Fighter archetype features to those of Rogue.
I did not compare archetype features, only base class features. If the archetypes are unbalanced, that is a different question, and we are then comparing subclasses. Arcane Trickster and Eldritch Knight are fairly balanced. I don't know the others. I am not trying to optimize builds but compare base classes.
We need to remember that the Rogue is likely spending their 4th level ASI most profitably on Dexterity, while the Fighter can take Shield Master (which expertise in Athletics will make godly, as an aside).
You point out that the Fighter could pick Shield Master or other feats. The rogue, too could pick a feat, like Sharpshooter or Magic Initiate. Or Trained. There are lots of options that a rogue can do other than trying to be just like a fighter. The rogue's Dex would match the fighters then, but he'd have new abilities to compensate.
Thieves' Cant is a ribbon - I'm surprised you're including it at all - but Fighter has it from Spy in any case.
The rogue also has a background, which evens out Spy.
Fighter out fights Rogue, and has an additional skill with expertise (five to Rogues' four).
The question most of all is what your design goals are? If it satisfies your design goals to make this feat much stronger and over-shadow Rogues, then you should do it.
I don't think that allowing class to taste a little bit of flavor from each other overshadows any of them. Each is still better at its specialties, and each still has a role to play in the game. All choices have trade-offs, and no class is strictly superior to any other. Even the much maligned Ranger is great at what it does if he isn't a Beastmaster (and not completely terrible there, either), and if exploration and difficult terrain are included in an adventure. If we are comparing any class to rogue for roguish skills, the ranger rather than the fighter would be most likely to overlap.
Picking out the fighter's extra ASI assumes that the fighter is overpowered to get that ASI at all. What about the rogue, the only other class that gets bonus ASIs? Are rogues overpowered compared to everybody else?
That's different from arguing that the feat is balanced or unbalanced. I think balance in RPGs is all about three things
1) Broaden options (make many different strategies viable)
2) Don't warp the narrative (nothing that forces every scenario to warp around it)
3) Let them shine (no overshadowing)
I think Trained narrows options by making Rogue less viable, while broadening options by giving other classes more to play with. My guess is, we lose more from loss of Rogues than we gain for other classes. Trained might turn out to warp the narrative, because it might pressure bounded accuracy. DMs might have to react by pushing up all their numbers. Finally, Trained clearly does not let Rogues shine. It lets Fighters (and other classes, no doubt) shine more, but for me the overshadowing of Rogues doesn't look well repaid because those other classes almost all already have their own ways to shine.
Trained definitely broadens options, for every class, but your critique focuses on narrowing options to optimize the fighter. Yes, Trained allows fighters to gain expertise and be more roguish, but it also allows rogues to get better in armor and weapons. Looking at the classes as a whole, this feat offers something to everybody.
Trained doesn't warp the narrative, except for the worry about bounded accuracy which should already exist with rogues as it is: this can be mitigated with the most recent alteration I made, limiting the amount of expertise you can take at one time. But rogues are still rogues, and fighters are still fighters. Each class has its place.
Nor does Trained prevent rogues from shining, as they are still the best at every skill with a minimum 10 roll. If anything, it allows the Rogue to be even more phenomenal in skills at large, and to allows the
Ranger to shine in its stealthy scouting, a core trait of the class!
It is vital to remember that each class is part of one character, but characters are on a
team. You should be balancing your party, not competing player-to-player.