EzekielRaiden
Follower of the Way
Because what actually matters is number of combat rounds between rests, not total number of combats per day, and hard encounters are not in general twice as long as easy encounters.
I've crunched the numbers. Champion Fighters are--sorta-kinda-ish--"balanced" with at least other Fighter subclasses IF they get enough combat rounds in the day. It's actually really easy to calculate their bonus damage, because it's 5% (or 10% at high level) of the amount of bonus damage rolled due to a crit. We can then take something like Battle Master, where we know more-or-less exactly how much bonus damage it should be doing (its total Expertise Dice per rest), and figure out how many combat rounds are needed to make up the difference.
Combats in 5e are generally quite short. Around 3 rounds in general, sometimes up to 5 for particularly deadly fights, sometimes less. However, because most monsters are big bags of HP, even "easy" combats tend to fill up at least the minimum time because you just have to chew through so many hit points.
At 3rd level, the Champion gets (on average) 5% of their weapon damage as bonus damage per swing, since critical hits only multiply dice, not static damage; at 15th level, it's 10% of weapon damage. Since the game was balanced without factoring in magic items, I will be ignoring their effects (though I will also be ignoring the effect of crits on maneuvers, which is actually the optimal way to use maneuvers, but I'm trying to be favorable to the Champion here.) For easier math, I'll consider both to be using a greatsword (with Great Weapon Fighting style, naturally). Feats are optional, so I won't be including them, though their benefit is technically irrelevant here since Great Weapon Master gives static damage and is thus unaffected by crits. A GWF greatsword does 8.33 damage on a hit.
3rd: 5% of 8.33 = 0.4165. BM has 4d8 = 18 average damage per short rest, so the Champion needs 43.2 attacks to match. Pretty clearly inferior at this level.
5th (EA1): No numerical changes, but by making 2 attacks each attack, we cut it down to needing only ~22 combat rounds between rests, which is still way too high, but almost kinda-sorta possible.
7th: BM now has 5d8 = 22.5 average damage, so unfortunately things get worse for our Champion, who now needs (22.5/0.4165)/2 = 54/2 = 27 combat rounds between rests.
10th (EA2): Now things get interesting. BM dice are now 5d10 = 27.5, but that's now (27.5/0.4165)/3 = 22 combat rounds. Fascinating, I hadn't expected this to literally balance things back out to where they were at 5th level!
15th: Now things get really interesting, Champ finally gets a damage bonus! Instead of 0.4165, it's 0.833 damage per swing. BM also gets another die, but that's a smaller change. 6d10 = 33, (33/0.833)/3 = 13.2. Holy crap, we actually have a number of combat rounds that is VAGUELY PLAUSIBLE...if they're long enough. At 2-3 combats per short rest, you need those combats to be at least 4 rounds, and that's a long combat by 5e standards.
18th: Aaaand we fall back off the wagon again because now those dice are d12s. 6d12 = 39. (39/0.833)/3 = 15.6. Ah well, it was good while it lasted.
20th (EA3): Just for completeness. (39/0.833)/4 = 11.7. Again, we're gonna need some long combats (~6 rounds if only two combats per rest, ~4 rounds if three.)
5th (EA1): No numerical changes, but by making 2 attacks each attack, we cut it down to needing only ~22 combat rounds between rests, which is still way too high, but almost kinda-sorta possible.
7th: BM now has 5d8 = 22.5 average damage, so unfortunately things get worse for our Champion, who now needs (22.5/0.4165)/2 = 54/2 = 27 combat rounds between rests.
10th (EA2): Now things get interesting. BM dice are now 5d10 = 27.5, but that's now (27.5/0.4165)/3 = 22 combat rounds. Fascinating, I hadn't expected this to literally balance things back out to where they were at 5th level!
15th: Now things get really interesting, Champ finally gets a damage bonus! Instead of 0.4165, it's 0.833 damage per swing. BM also gets another die, but that's a smaller change. 6d10 = 33, (33/0.833)/3 = 13.2. Holy crap, we actually have a number of combat rounds that is VAGUELY PLAUSIBLE...if they're long enough. At 2-3 combats per short rest, you need those combats to be at least 4 rounds, and that's a long combat by 5e standards.
18th: Aaaand we fall back off the wagon again because now those dice are d12s. 6d12 = 39. (39/0.833)/3 = 15.6. Ah well, it was good while it lasted.
20th (EA3): Just for completeness. (39/0.833)/4 = 11.7. Again, we're gonna need some long combats (~6 rounds if only two combats per rest, ~4 rounds if three.)
Technically, I also left out the feature that grants more expertise dice when you roll initiative without any, but I willingly ignored that because it's not particularly great as a feature anyway.
So...as you can see, the Champion is supposed to be getting TONS of combat rounds if they're meant to keep up with even other Fighters, let alone more powerful classes like Paladin. That's why the game is built around having tons and tons of encounters. You need them in order to let the Champion catch up and in order to bleed off the enormous pile of daily resources given to full casters.
