In case you were confused, the title of the thread is "Fixing the Terrible Weapon Master Feat". So, the question you pose isn't any different than the reasons someone would take the original feat. Multiclassing isn't allowed; playing to level 20 and don't want to give up a capstone ability through multiclassing just to get a weapon; gain access to weapon proficiencies [Did you want a "not" here"? in the base table.
So, what I am assuming you meant was that you don't think the proposed change is sufficient to make the feat viable. Fair enough. But maybe offer your own tweak or build on what others have posted.
Yeah, I don't think it is sufficient enough for most tables.
From everything I have seen and heard 1) Multi-class is common, 2) Most capstones are not desirable 3) Most tables do not use weapons not on the base tables, and if they do they often either provide proficiency or the DM does not want players proficient in those weapons.
I did offer the homebrew I use (taken from The Dawnforged Cast) earlier in the thread, it led to a sizable debate so I'm not inclined to try a second verse of the same thing.
Thinking on it though, I don't think I would attempt to "fix" the feat by changing the single feat. Off the top of my head, I can't think of one balanced ability that would make sense for someone who is a master of all weapons to have. It would fit the design space better to work with making feats that cover all sorts of styles and weapon choices.
I also think, that the majority of those feats should be highly desirable by Fighters, Barbarians, Paladins and Rangers, the four classes most strongly tied to the martial archetype. The biggest issue I have with your proposed fix of adding a fighting style is that most of these classes already took their fighting style by the time they get this, and the majority of fighting styles are exclusive. It can be really enjoyable to have an ability that gives you a little more flexibility, but for most of these classes it will work out as +1 AC for taking defensive, because that style isn't most people's first choice but it is a major second choice.
Looking at medium armor mastery, it also gives a +1 AC, but the major draw in my eyes is actually the ability to negate the disadvantage on stealth checks (which sneakily also increases AC, since it means players will move from Breastplate to Half-plate) which is an ability the PC did not have the option of taking before.
And that is the core of feats to me, the ability to do something you could not do before.
Weapon Master
Select two weapons, which are your mastered weapons. You gain the following benefits.
- You are proficient with your mastered weapons.
- You gain the benefits of a fighting style when wielding a mastered weapon. These fighting styles do not stack with the same fighting style gained from another source.
--- If the weapon has the two-handed keyword, you gain the Great Weapon Fighting Fighting Style.
---If the weapon has the light keyword, you gain the Two-Weapon Fighting Fighting Style.
--- If the weapon is a ranged weapon, you gain the Archery Fighting Style.
--- For any other weapon, you gain the Dueling style.
- Before you make an attack with a mastered weapon, you can choose to take a -5 penalty to the attack roll. If the attack hits, you add +10 to the attacks' damage.
I like the idea behind this, but I'm thinking about how it would work in implementation.
Paladin or Fighter with a greatsword took the Great Weapon Fighting Style at levels 1 or 2, so at level 4 they are looking at a feat that gives them a style they already have, proficiency in the weapons they already have proficiency in, and can take the -5/+10 of Great Weapon Master...
Or they take Great Weapon Master, get the -5/+10, and the ability to make bonus action attacks under certain criteria.
Fighter or Ranger with a bow... same story. They likely already took Archery, and this is a worse source of the -5/+10 than the Sharpshooter feat.