+1 to crit doubles the number of times that you get critical damage. Add on proficiency and the Champion can be rolling in the damage. I saw a low-level Champion using TWF, and he did more damage than the rest of the party put together, at least until he got turned to stone by a Basilisk.
Er...Proficiency has nothing whatsoever to do with whether you crit. Nothing at all. And, unless I'm mistaken, Proficiency is never added to damage rolls. So I don't see why the Champion would be "rolling in the damage" in comparison to any other Fighter archetype. Critting 10% of the time instead of 5% equates to 5% bonus damage on average, but in a very "spiky" way. Maneuvers have limited numbers of uses, but work much more consistently (particularly for the best maneuver, which makes you hit more frequently, thus producing very
consistent damage).
I have to say that the Champion is fine. It isn't, you know, very exciting as a mechanical concept, but that is exactly the point. The class is fun, and if there is a problem within the Fighter class, it is more to do with annoying combinations between Battlemaster abilities and certain feats (trip-fighters have never been fun for me as a DM, regardless of edition).
I understand the impulse, but I see it as misdirected. The Champion is definitely meant to have a "I don't want to think about
anything mechanical" nature. But it really should've picked up some of the slack in the non-combat areas as a result. Remarkable Athlete is
slightly better than getting an Artisan Tool prof, but not much...particularly when Champs would already be pretty damn good at most of those ability checks anyway. It's certainly not very "remarkable" particularly when *all* Bards get something strictly better (if you ignore the, IMO almost-meaningless, extra jump distance).
I wouldn't call the Champion a
strong class. It's not a "trap option," which is a meaningful thing, but borders on damning with faint praise. It's better than the Beastmaster Ranger...which is again damning with faint praise.
I've run the numbers in a very simplistic excel sheet, and I think the champion is fine at level 10 and up, when they get a little lead in survivability by having +1 AC and then regeneration later. Until level 10, though, they lag behind in damage. Remember, at 3rd level, the Champion gets, at the most basic, +4d8 damage per short rest. In order for a greatsword wielding champion to do that, they'll need to get 2.16 crits more than the battle master. The battlemaster has a 5% crit chance, and the Champion has an extra +5% crit chance; they'd have to make 43.2 attacks per short rest for that damage to match up, and that's entirely ignoring the other utility of the battlemaster's extra damage. I'm not even looking at the more situational extra attack battlemaster maneuvers like Repost.
But I don't think the problem is entirely the Champion's. I think the problem is the Battlemaster starting with 4 superiority dice. The feat gives 1 superiority die. The monk starts with 1 ki point, which is arguably as useful as a superiority die until they get stunning fist (as it grants 1d4/1d6+ability attack, which can miss, unlike the superiority damage most of the time). If you compare the single target damage of the Battlemaster against the single target damage of the Eldritch Knight, or even the multitarget damage of the Eldritch Knight, the Battlemaster again looks just a little too good.
I don't think the Champion is that far behind. Again, they seem perfectly fine, if not geared for a little more defense, at level 10 and above. I think the Battlemaster should have less dice to start off with, and then they can gain them faster and end at the same point. They regain their dice after every short rest, so they could start with 1 and gain 1 again at 6, 9, 12, 15, and 18.
Eugh, no, don't tank the Battlemaster to bring it into line with the Champ. Particularly not by giving it ONE die per short rest to start with. You do realize that that would mean Warlocks would have more spells than Battlemasters have maneuvers until level 6, right? And that, with the assumed encounters-and-rests per day, that would mean getting to do
anything other than basic attacks only ~3 times per day (probably fewer, since all the evidence I've seen points to groups being fairly short rest averse), over the course of 6-8 fights. Wow, super exciting, getting to do ONE thing every other fight,
at best!
Much, much better to do a mixture of reducing the size of the die (to d6, because d4s would just be pitiful) and the number (probably to 3? That still feels scanty but perhaps it should). Expected value of 3d6 is 10.5. With three rounds per combat, six combats per day (aka, a low estimate), both Fighters should be making 18 attacks minimum, 36 at level 5. So the Battlemaster pulls slightly ahead for two levels--5e doesn't care about that sort of imbalance, just look at the Moon Druid. At level 5, you're looking at anywhere between 36 attacks (a day that favors the Battlemaster) and 8*5*2 = 80 attacks (a day that favors the Champion). Champion should expect approximately 3.5-8 crits per day; Battlemaster should expect half that, so 1.75-4. For a big weapon (since we're optimizing damage), that's either 2d6 or 1d12 times those values, so 7*(1.75) to 7*(4) = 12.25 to 28 bonus damage for the Champ, vs. a typical top-end of 3*3*3.5 = 31.5 extra damage for the Battlemaster's maneuver dice and a typical low-end of 1*3*3.5 = 10.5 extra damage.
So, if the BM gets more than 1 rest per 2 encounters, it'll pull ahead slightly, given the above changes. If it gets less than 1 rest per 2 encounters, it'll fall behind. Completely within 5e's acceptable "balance" range. Not that I think 5e actually cares that much about balance of this kind (again, looking at the Moon Druid).
If you're still really worried about the Battlemaster pulling ahead of the Champion, just have it deal +1 extra damage per crit. Originally I was going to suggest adding half proficiency, but that got wonky at max level (four attacks per round plus tripled crit range leads to LOTS of crits). That one extra damage piles up after a while (a max-level Champion can expect around 18 crits per day), and at the low levels it's enough to boost the Champ to be on par with, or even exceed, the Battlemaster. Who also has to worry about whether or not he gets two rests per day--and most of the evidence I've seen suggests the majority of them will be under-rested.