I agree that GWM is a massively overrated feat. When you math it out, it's really not that great. The 2024 version is an improvement.
The problem is not that the feat in isolation is powerful. The problem is that it combos with absolutely anything that boosts your accuracy, and the more accuracy boosts you can scrounge, the better it gets.
Take a 5th-level barbarian with 18 Str, a greatsword, and a 65% base chance to hit. Reckless Attack improves your hit chance to 87.75%, with a 9.75% chance of a crit. You average 2d6 (base greatsword) +4 (Str) +2 (rage) = 2d6+6 or 13 damage per hit, +7 on a crit, with two attacks. Factoring in accuracy and crits, you average 24.18 damage.
What happens if you drop Str to 16 and pick up GWM instead? Base chance to hit drops to 35%, but Reckless Attack brings it back up to 57.75%. Average damage per hit is 22, +7 on a crit. Crit chance is still 9.75%, but in addition to damage, you get a bonus attack on a crit; with two attacks, this has an 18.55% chance to trigger each round. (Bonus attack also happens on a kill, but I'll assume that cancels out the times you don't have a bonus action free.) Work it all out and you get 29.26 damage per round, or a 21% increase. That's the baseline for what you, the barbarian player, can get from the PHB on your own, and it's already quite respectable.
But what if there's a cleric in the party who casts
bless? Both barbarians benefit, but the improvement to a regular barbarian -- who was already hitting 7 attacks out of 8 -- is small: Your DPR becomes 25.92. A GWM barbarian, however, shoots up to 35.81! The net benefit of GWM in this scenario is +39% DPR.
What if you find a magic weapon? With a +1 greatsword, it's a 25% DPR advantage for GWM; with a +1 greatsword and
bless, it's 42%.
And in any situation where you are comparing GWM to other feats instead of to +2 Str (say variant humans are allowed, or you reach 12th level), it gets absolutely nuts. If this 5th-level barbarian is a variant human, the benefit of GWM is +39% DPR before we even consider magic weapons or spells. That's the bar another feat must reach -- if not in raw damage, then in overall tactical benefit -- to be worth taking over GWM. With a +1 greatsword and
bless, it's +56%.