I don't see how anyone can argue that GWM is improved - can you link the math on that? I'm looking thru Treantmonk videos but only found one old one using some bad assumptions (Champion fighter, no advantage). GWM currently adds WAY more than 3-6 damage per round under most builds, which is the max you can get with the new GWM (if the UA I'm looking at is still correct...)
Also how do you figure that weapon mastery substantially increases DPR? Increased utility is obvious, but only Nick really helps DPR and that's specifically for underpowered two-weapon fighting (which needs a big buff to even be worth considering). Cleave is awesome in rare situations but most of the time will do nothing. Graze brings up average DPR a bit, but doesn't help ceiling damage at all. And then all the rest of the masteries are utility only with no damage - you could argue that some help gain advantage more easily, but advantage is already guaranteed in any build that is properly designed.
Most people think the current iteration of GWM is good because most people are bad at math. Sorry, but it's true. It's good in the way that slot machines are good: occasionally there's a big, memorable payoff, but mostly you'd be better off doing something else. It's bad because the penalty (-5 to hit) is multiplicative, while the bonus is additive.
I'll defer to
@ECMO3 for the real details, but here's a basic example. Imagine a level 20 fighter taking on an Ancient Red dragon. We'll assume the fighter has +5 strength and a +3 weapon, because level 20. The dragon is AC22.
In this basic example, the fighter using GWM does 10 average damage per attack ((2d6=7+3+5+10)x.4). I won't bother with criticals; they don't change the math much. Without GMW, that same fighter does 11.25 damage per attack ((2d6=7+3+5)x.75)).
And the thing is, because the penalty is multiplicative but the bonus additive, the more additional damage sources that fighter can add to each hit, the worse GWM becomes. Let's say the party cleric casts holy weapon on the great sword. With GWM, the fighter now does 13.6 damage per attack ((2d6=7+2d8=9+3+5+10)x.4)). Without, they do 18 damage per attack ((2d6=7+2d8=9+3+5)x.75)).
If they action surged to do 8 attacks in the crucial first round, GWM just cost them 35.2 damage.
The new version of the feat gives a +1 strength bonus, which helps all martial classes that would choose this feat, and is always a damage increase, in every situation. Overall, it's a much better feat. The current GWM is just fun for gamblers.
As for weapon masteries, most of those "utility" properties add up to straight damage increases. For example, being able to knock an enemy prone with your attack is usually a massive DPR increase for your entire party.
Have you play tested with the new abilities? I have, extensively, and so have plenty of others, such as Treantmonk, and show their math. Martial DPR goes WAY up using the 2024 rules.