I'm a couple of days late checking this thread but will give some thoughts on the topic in general as well as address some of the specific examples brought up.
I remember how powerful an extra fighter or two could be in Baldur's Gate 2
BG2 didn't function like a traditional D&D game/party. Not only if the protagonist literally powered by the Divine but almost every single companion has some unique twist that makes them stand out from their actual class and subclass.
Minsc is more than just a Ranger, if he even is one because he functions more like a Fighter. His internal party interactions can lead him to adopt Aerie as his new witch after the death of Dynaheir between BG 1 and 2 which will lead to moments where Minsc can enter a berserker rage, despite not being an actual Berserker, if Aerie gets hurt too much. There is also Boo, who turns out to be exactly what it says on the tin. A miniature giant space hamster, and not just a regular hamster some brain adled strongman has been convinced otherwise. Most Rangers don't get played like this, Minsc functions better as a two handed tank/dps than the animal attuned archer/"ranger" stereotype or dual wielding swords type and apart from the protagonist, Keldorn, Sarevok, and a couple of others, Minsc potentially one of the single best melee characters you can get. As a Ranger.
Speaking of Sarevok, he's quite possibly the best melee character in the game again because of unique traits which also require several significant decisions to be made in order to make use of them.
First, you need to resurrect him in Throne of Bhaal and recruit him. Second, you need to give him his sword back, a sword you originally get all the way back in the very first dungeon in BG2, but only if you do the side quest for the Djinn and return its lamp from Irenicus' chambers. Then you have to hold on to the sword for the entirety of BG2, although others can use it in the meantime, because it's not until ToB where giving it back to Sarevok will let him return some of its lost power and upgrade it from a +2 2h sword to a +4 that only Sarevok can then wield. By this point in the trilogy you should be able to take epic levels which means whirlwind and greater whirlwind in the case of Sarevok, and Minsc. Add on to that Sarevok's Deathwalker ability where he can literally one shot almost anything and you can see why he's the best melee character in the game outside of the protagonist who only beats him due to both plot and broken class choices.
And those broken class choices are a multiclassed Kensai/Mage that gain martial abilities from the Fighter subclass in addition to armour bonuses that don't need actual plate, the aforementioned WW and GWW epic feats, and access to various Mage spells to further increase your abilities as well as simply cause damage should you so wish. Or even Wish. Simulacrum, Contingency, and others like Haste, Mage Armour, let you further buff yourself to absurd levels because the game design accidentally permits it, but then you're meant to be a demigod according to plot so acting like one this way isn't really that out of character.
It's the same error Dragon Age Origins made with the Mage subclass Spirit Warrior that permits Mages to use their INT stat to work for both melee weapons and wearing armour when it would otherwise require STR. You can then again couple martial and magical abilities for a synergy that outperforms everything else in the game.
Similar to being powered by the Divine in Baldur's Gate, Mages in Dragon Age really are that terrifyingly powerful so again it's still more or less behaving in line with how the class can be for plot reasons.
I have some MMO examples to go over as well which I'll do in a separate comment.
I'm a couple of days late checking this thread but will give some thoughts on the topic in general as well as address some of the specific examples brought up.
BG2 didn't function like a traditional D&D game/party. Not only if the protagonist literally powered by the Divine but almost every single companion has some unique twist that makes them stand out from their actual class and subclass.
Minsc is more than just a Ranger, if he even is one because he functions more like a Fighter. His internal party interactions can lead him to adopt Aerie as his new witch after the death of Dynaheir between BG 1 and 2 which will lead to moments where Minsc can enter a berserker rage, despite not being an actual Berserker, if Aerie gets hurt too much. There is also Boo, who turns out to be exactly what it says on the tin. A miniature giant space hamster, and not just a regular hamster some brain adled strongman has been convinced otherwise. Most Rangers don't get played like this, Minsc functions better as a two handed tank/dps than the animal attuned archer/"ranger" stereotype or dual wielding swords type and apart from the protagonist, Keldorn, Sarevok, and a couple of others, Minsc potentially one of the single best melee characters you can get. As a Ranger.
Speaking of Sarevok, he's quite possibly the best melee character in the game again because of unique traits which also require several significant decisions to be made in order to make use of them.
First, you need to resurrect him in Throne of Bhaal and recruit him. Second, you need to give him his sword back, a sword you originally get all the way back in the very first dungeon in BG2, but only if you do the side quest for the Djinn and return its lamp from Irenicus' chambers. Then you have to hold on to the sword for the entirety of BG2, although others can use it in the meantime, because it's not until ToB where giving it back to Sarevok will let him return some of its lost power and upgrade it from a +2 2h sword to a +4 that only Sarevok can then wield. By this point in the trilogy you should be able to take epic levels which means whirlwind and greater whirlwind in the case of Sarevok, and Minsc. Add on to that Sarevok's Deathwalker ability where he can literally one shot almost anything and you can see why he's the best melee character in the game outside of the protagonist who only beats him due to both plot and broken class choices.
And those broken class choices are a multiclassed Kensai/Mage that gain martial abilities from the Fighter subclass in addition to armour bonuses that don't need actual plate, the aforementioned WW and GWW epic feats, and access to various Mage spells to further increase your abilities as well as simply cause damage should you so wish. Or even Wish. Simulacrum, Contingency, and others like Haste, Mage Armour, let you further buff yourself to absurd levels because the game design accidentally permits it, but then you're meant to be a demigod according to plot so acting like one this way isn't really that out of character.
It's the same error Dragon Age Origins made with the Mage subclass Spirit Warrior that permits Mages to use their INT stat to work for both melee weapons and wearing armour when it would otherwise require STR. You can then again couple martial and magical abilities for a synergy that outperforms everything else in the game.
Similar to being powered by the Divine in Baldur's Gate, Mages in Dragon Age really are that terrifyingly powerful so again it's still more or less behaving in line with how the class can be for plot reasons.
I have some MMO examples to go over as well which I'll do in a separate comment.