dnd 5e – What problems might occur with this variant Advantage / Disadvantage?

In the player's manual, it is specified that the Advantage and Disadvange sources "cancel" effectively regardless of their number:

If the circumstances give a result an advantage and a disadvantage, it is considered that there is none and you get a d20. This is true even if several circumstances impose a disadvantage and only one grants a benefit or vice versa. In such a situation, you have neither advantage nor disadvantage.

Intuitively, this rule makes sense, but it has very strange mechanical consequences, especially with regard to several Disadvantages (which is much more common than many Advantage sources).

Take, for example, creature A pulling a Longbow of 550 on its target (conscious and engaged in combat), creature B:

  • From 550 'distance, creature A has a source of disadvantage
  • SOcreature A has a disadvantage on his attack roll

Let's now look at the scenario where this same creature A first enters a thick fog area before attempting to fire and can no longer see its target (and conversely, creature B can no longer see creature A). They are still aware of the location of creature B (because creature B has not moved yet), but they can not see them anyway.

  • From 550 'distance, creature A has a source of disadvantage
  • Unable to see its target, creature A has a source of disadvantage.
  • Unable to see his attacker, creature A has a source of Advantage
  • SO, creature A has no advantage or disadvantage on his attack roll (???)

Do you see the problem? By doing something that, by any objective logic, should have made the shooting more difficult by obscuring the vision of their target, they have rather simplified their shooting; Blinding has resulted in a significant improvement in the accuracy of their shooting.

To solve this problem, I propose to allow several Disadvantages to take precedence over a lower number of Advantage sources. This rule would not be symmetrical; it would not be possible to gain an advantage with any number of sources of disadvantage. That's my proposal [re-]the wording of this paragraph:

Variant – Several sources of advantage or disadvantage. If circumstances make a role present both an advantage and a disadvantage, compile the sources of advantage and disadvantage conferred on that role. If the number of Disadvantages sources exceeds the number of Advantage sources, the disadvantage result is Disadvantage. Otherwise, the jet is made without any advantage or inconvenience; to have an excessive number of sources Advantage will not give an advantageous result.

The purpose of this rule is to prevent characters from performing strange "trick shots" like the ones I described above, in which a course of action that should logically make an action more difficult makes it easier.

Are there common / noticeable situations in which this decision could be against you? If so, what are these circumstances?

Why not symmetrical?

The short version is that Advantage, for me, represents the circumstances where a character is particularly capable to perform any task that they are trying to perform, that it is to escape from the explosion of a fireball or succeed in shooting with an arrow. If certain circumstances interfere with their ability to do so, even if they receive a lot of bonuses, their interference should usually cancel anything that is easy for them.