First off, thanks for the recap.
Improved Critical barely adds additional damage. It's just 1 additional crit every 20 attacks.
Agreed. The only way this becomes decent if for builds that crit-fish, which is definitely not something "simple" to build or comprehend for new players--especially younger players. A simple "weapon specialization" feature (+1 to attack or damage with chosen weapon) would be better IMO.
On the plus side, new players who roll that 19 and get a critical are really happy when it happens, and that makes them feel like it was a good choice.
Remarkable Athlete barely does anything. +2 for a few checks.
The problem with this is a Rogue with expertise is better at Athletics than a Fighter with Remarkable Athlete because the fighter typically already has this proficiency. Expertise in Athletics or allowing the feature to benefit even if already proficient would be better.
However, not many fighters take Acrobatics, Stealth, or Sleight of Hand, so gaining some benefit to Acrobatics and Stealth is good, but it is hardly stellar.
Constitution "checks" are not common IME, either.
Additional Fighting Style barely does anything because fighting styles only affect one type of weapon. If you take GWF, no other FS will affect your greatsword Except Superior Technique
I can't quite agree completely on this. I see your point, however. Even if you start with GWF, Defense for a +1 AC is helpful and simple, and since AC is difficult to improve this is pretty good as I see it. Defense is also a good addition if you begin with Archery or Two-Weapon Fighting since you can't use a shield.
Obviously, if you are a sword/board build, combinations of Dueling, Defense, and Protection can all be good.
In easier terms, there isn't enough design space to be good AND simple.
A class has 20 levels to build a concept. A subclass only 5.
Any decent designer could create a simple warrior with 20 levels to work with.
Few can do so with 5 when you are already stuck with the fighter chassis.
Well, I think this is enough though. Fighters have more sublcass levels than any other class since most have 4 and Bards only 3. And there is really nothing wrong with the fighter chassis as it does what is needed with two additional ASIs. Now, if feats aren't used (very rare IME) then it looses something, but otherwise it is simple and solid.
Like someone said, you could easily make simple warrior with just flat damage bonuses.
But a fighter subclass is only allowed 5 levels to do this.
Makes it harder. WOTC tried with the Brute and it blew the Champion out the park so bad it was abandoned.
A full class has 20 levels. Especially if you want it to be simple and only have 1 class feature per level.
Since damage is key (as mentioned) a simple +1 damage per subclass level would result in an additional +5 by the end.
Obviously, I don't have the same issues with it you do. I definitely agree there is room for improvement, but I believe it is possible to have Champion simple, effective, and remain under the Fighter class.
Again, thanks for the summary.