Dual Wielder feat combined with Light property allows up to 2 extra attacks using TWF (so at level 5 that is 4 attacks total). This is explicitly how the wording is RAW, stating it is an "extra attack" and it is RAI as confirmed by Jeremy Crawford that Dual Wielder gives another attack on top of the Light weapon property attack (if applicable) when the Dungeon Dudes asked him at Gen Con.
I took that into account. 4 attacks per turn at 5th level is only 1 more attack per turn than any martial character using two Light weapons can make without the Dual Wielder feat, so my assessment of the Feat increasing your DPR by 1d8 (1d10 or 1d8 with a shield with weapon swapping cheese) is accurate.
RAI you are supposed to be able to go for example with twin shortswords, one in each hand, and go 2 attacks as an action and 2 more attacks as a bonus action if you have the dual wielder feat.
Well, no, you’d need at least one of the weapons to be a scimitar, and to have used one of your weapon Masteries for scimitars. You can’t use your bonus action to attack with the Light property
and use your bonus action to attack with Dual Wielder. However, you can use the Nick Mastery to attack with the Light property as part of the Attack action and use your bonus action to attack with Dual Wielder. The other Light weapon can be a shortsword though, which is probably optimal.
This is confirmed RAI and even this simple example will outrun PAM I think. PAM with a d10 weapon is doing 4 more on the attack action but 4.5+STR less on the bonus action.
You’re comparing apples and oranges.
At 5th level, a glaive, halberd, or pike user is doing 5.5+Str and applying their mastery effect on each of two attacks, for a total of 19 DPR, assuming 18 Strength. A scimitar and shortsword user at the same level with the same Strength or Dex Mod is doing 3.5+Str or Dex and applying Vex on each of two attacks and 3.5 on their Nick attack, for a total of 18.5 DPR. Half a point less damage, but more consistently due to it being split between three attacks and two of those attacks being made with advantage, but at the cost of not getting to apply an on-hit effect like Graze, Push, or Cleave, and at a 5 foot reach instead of 10. Both characters still have a bonus action available.
Add on PAM, and the polearm user gets another attack with their bonus action, dealing 2.5+Str damage (so +6.5 total in our example), and they get a third application of their mastery effect. Likewise the two-weapon user can make another attack with their bonus action if they take DW, which can be with any weapon that lacks the two-handed property, but they don’t add their ability mod to that damage, so it’s +4.5, assuming they use a rapier for dex or a longsword for str. No extra mastery effect, since this strategy already uses both mastery slots on scimitar and shortsword. If you want to assume the two-weapon user is abusing the weapon swapping cheese, they can make that +5.5
if they’re strength based by two-handing the longsword, or they can stick to +4.5 and end up with a shield equipped.
Far from outshining the PAM user’s DPR, the PAM user actually pulls further ahead by 1 DPR, even assuming weapon swapping cheese (or pulling 2 points ahead and falling 2 AC behind if the dual wielder uses weapon swapping cheese for a shield instead of a versatile weapon).
This is all before accounting for Fighting Styles, of course. If we also consider Fighting Styles, the dual wielder gets an extra 8 DPR from the Two-Weapon Fighting style (+Mod to the two attacks that didn’t benefit from it), while the Polearm user doesn’t benefit as much in the DPR department, getting only about +1.05 DPR from the Great Weapon style. However, the wise PAM user knows the Great Weapon style is garbage, and instead opts to use a spear and shield instead of a glaive, halberd, or pike, and takes the Dueling style. That trades their d10 damage die for a d6+2 (a wash in terms of DPR) and gives them a shield for their trouble. The +2 damage from dueling will also apply to the 1d4 butt attack from PAM, so this actually increases their DPR
and their AC each by 2, at the cost of losing Reach.
The net result is that the two weapon user does 3.5 more DPR than the spear user (5 with weapon swapping cheese), but the spear user gets 2 more AC (or equal AC and only 2.5 less DPR with weapon swapping cheese to get a shield). So, yeah, all told, dual wielding is theoretically a
little stronger than polearm use. But only by a few points of damage, and that’s easily made up for by the polearm user getting more consistent reaction attacks. So, yeah, pretty comparable overall.
