One could argue that draconic bloodline sorcerers are farther removed from dragons than dragonborn.
Actually, no.
Draconic bloodline sorcerers are specifically manifesting the powers of literal dragons. They might be distantly related, but their manifestation is explicitly based on actual full on dragons (Which is why they exhibit many actual dragon features. Dragon scales, claws, wings etc)
Dragonborn are simply manifesting Dragonborn features, which are distantly related to dragons but have been watered down through that distance.
Which one would you call mental gymnastics?
2. Dragonborn don't have scales. Obviously. Duh.
I mean, we're not even having the same discussion. I'm saying it was poorly designed and you're saying dragonborn don't have scales. As if dragonborn were real. Simply put, it makes for a better setting if dragonborn do have scales and those scales provide a similar AC to the draconic sorcerer's scales. As opposed to having debates about whether or not dragonborn have scales.
This is a prime example of mental gymnastics.
I never said Dragonborn don't have scales. I said they don't have HARD DRAGON SCALES.
As I mentioned, scales aren't inherently tough. There are obviously different kinds of scales. Dragons, actual true dragons, have tough scales that provide them with a lot of defence (19 base AC for adult dragons. 22 base AC for ancient dragons)
Dragonborn might have scales, but it's not necessarily true that they're as hard as actual dragon scales. If we consider the mechanics as an indicator then it is suggestive that they're soft scales that provide no AC bonus.
Draconic Sorcerers manifest actual HARD DRAGON SCALES and so they get an AC bonus due to the protective nature of such hard scales (It's limitation to 13 AC is likely due to the fact that they only have a partial covering of scales. Whereas a Dragonborn is covered head to toe in scales which would indicate some level of increased AC if they were HARD DRAGON SCALES)
Thus there is no natural precedent for the "Flavour" of Dragonborn having increased AC, if the case is that they DON'T have HARD DRAGON SCALES and instead have soft scales that provide no AC bonus.
If anything, the most obvious flaw in "Flavour" design is with Draconic Sorcerers. Whom will lose their innate AC bonus if they wear a thick shirt. As if simply donning some clothing makes their scales soft. Due to the functionality of their bonus being akin to the Mage Armour spell and thus incompatible with worn armour. If we had accurate flavour, their AC would always be a base of 13 (Plus Dex mod) even if wearing armour.