Personally, I think a lot of theses posts asking for buffs to Dragonborn are asking for too much. Getting resistance to elemental damage is already a huge boon.
The argument that dragonborn should have the same abilities as dragons falls flat to me. These are attempts to make dragonborn overpowered relative to other races.
For humanoids, I think only Underdark races (drow, duergar, deep gnomes) should have dark vision. It really doesn’t make sense for surface dwellers to have dark vision unless they are also nocturnal and normally are only awake during the night.
I think a +1 bonus to AC or well scaled breath weapon are good options. However, I think it would be unbalanced to give them both abilities.
Before getting into Dragonborn themselves. Did you even look at or consider the other races before making this comment? 1 resistance is a huge boon as if that's enough by itself? Tieflings get fire resistance, darkvision, and innate spell casting that has quality spells as options. Shield Dwarves get an entire extra stat point and poison resistance and advantage on poison saves. Gold dwarves get the same deal with poison but also +1 hp per level, and both dwarves get darkvision to boot.
So regardless of who you feel should and shouldn't have darkvision. Races that have them do and Elves and Dwarves had "low-light" vision in 3rd and 4th edition and you know what Dragonborn did too so why did they have it taken away?
So first to do with Dragonborn. The breath weapon as is, is not a boon but a pretty bowtie as its worse than doing literally anything else that you could possibly do in almost every situation.
Second. Dragonborn descended from dragons so it is a valid arguement. Its a matter of knowing lore. Plus in prior editions Dragonborn had the same vision as Elves and Dwarves. It was called low light vision and was not as good as dark vision that only monster races and underdark races had.
Third. They only have 2 types of vision in this game. So if they limited darkvision as you said then the TTRPG would be heavily imbalanced towards the very few races with darkvision considering the disadvantages from not having it are huge.
Tieflings have useful innate spell casts, fire resistance, and dark vision. So how would it be too much for the dragonborn to have 2 useful traits beyond their resistance exactly? If you don't value Darkvision as highly as +1 to AC then you don't understand the actual value of Darkvision.
People really need to consider the actual strength that some races bring before saying that asking for darkvision and a better breath weapon is asking for too much. OH and not every race would have Darkvision giving it to Dragonborn. Humans and Halflings still wouldn't.
It becomes very apparent who in these forums have played D&D long term, played short term, and not played at all. As varying degrees of understanding racial histories and lack there of understanding the value of proper racial balance is showing.