You folks really would've burned Baldur's Gate 1 and 2 to the ground if this little mix-up to the numbers game is bothering you.
I feel like you saying that indicates you didn't read the actual main post since you seem to think providing Advantage/Disadvantage on every single attack without cost is relevant, so I copied it here for you:
The Maths: - In 5e, in general, having Advantage is roughly equivalent of having +5 to your roll. Disadvantage is roughly equal to having -5 to your roll. This means if one character is rolling with Advantage, and the other character is rolling with Disadvantage, then there is the rough equivalent of +-10 between their rolls. Additionally, Advantage doubles the chance of rolling a critical hit, and makes critical failures much less likely (5% normally vs 0.25% with Advantage), vice versa for Disadvantage.
Next, one of the core theories for game balance in 5e is called "Bounded Accuracy". This term means that players and NPCs generally have limits to how high they can boost their static modifiers to rolls. There is a 'bound' on just how 'accurate' a player can become. This was a huge shift in D&D when it was introduced. In prior editions of D&D, players could achieve truly insane modifiers to their to-hit, to the point where attack rolls were reaching into the 1d20+100 range, which just creates stupid arms races between monsters and players. By reducing how much a player can add to their to-hit, WotC (the publishers the D&D rules) made smaller bonuses much, MUCH more important. For example, Bless requires both a spell slot, concentration, and is limited to three targets, and only provides an average of +2.5, half of Advantage.
Bounded Accuracy is why Adv/Dis is so impactful on gameplay. There are a few class abilities that can add a higher static modifier (such as a War Cleric's Channel Divinity that can add +10 to one single attack roll) but those are rare and always limited in amount. It is a large reason why 5e is generally much more balanced that prior editions of D&D with far less ways to truly 'break' the game. It also makes the gameplay much smoother because enemies to-hit and AC do not need to increase as much as you get higher level. On page 274 of the DMG, there is even a chart for rough AC numbers based on a creature's CR (Challenge Rating. The higher the CR, the more 'powerful' the creature):
CR 0-3: 13 AC CR 4: 14 AC CR 5-7: 15 AC CR 8-9: 16 AC CR 10-12: 17 AC CR 13-16: 18 AC CR 17+: 19 AC
Look at those numbers. Over the course of 17 'levels' of CR, the enemies AC only increases by an average of +6. Just having Advantage almost cancels that growth out entirely. Here is an analysis of the actual monsters made available from WoTC and their respective change in AC -> https://i.stack.imgur.com/a6rlg.png
Lastly, if you take a level 1 character and a level 17+ character, give them the same stats and the same weapon, the total difference in their to-hit roll will be....+4. That's it. A level 1 character has a proficiency bonus of +2 and a level 17+ character has one of +6. The difference between these otherwise the same characters is less than the difference from Adv/Dis. That is how strong Adv/Dis is mathematically.
Hopefully by now, you can see why getting Adv/Dis is such a huge deal in 5e rules, and why being able to have them should be considered such a huge impact on the mathematics at play.