It's not quite.So what is WoTC's excuse for nerfing the Dragonborn's Breath Weapon back to the PHB version? curious
PHB: When you use your breath weapon, each creature in the area of the exhalation must make a saving throw, the type of which is determined by your draconic ancestry. The DC for this saving throw equals 8 + your Constitution modifier + your proficiency bonus. A creature takes 2d6 damage on a failed save, and half as much damage on a successful one. The damage increases to 3d6 at 6th level, 4d6 at 11th level, and 5d6 at 16th level.
Fizban: When you take the Attack action on your turn, you can replace one of your attacks with an exhalation of magical energy in a 30-foot line that is 5 feet wide. Each creature in that area must make a Dexterity saving throw (DC = 8 + your Constitution modifier + your proficiency bonus). On a failed save, the creature takes 1d10 damage of the type associated with your Chromatic Ancestry. On a successful save, it takes half as much damage. This damage increases by 1d10 when you reach 5th level (2d10), 11th level (3d10), and 17th level (4d10).
UA: As an Action, you exhaledestructive energy in a 15-foot cone. Each creature in that area must make a Dexterity saving throw against a DC equal to 8 + your Constitution modifier + your Proficiency Bonus. On a failed save, a creature takes 1d10 + yourcharacter level in damage of the type determined by your Draconic Ancestry trait. On a successful save, a creature takes half as much damage.
Assuming averages, at first level, a dragonborn does 7 points (PH), 5.5 points (Fizban), or 6.5 points (UA). At 5th, this increases to 10.5 (PH), 11 (Fiz), and 10.5 (UA). At 11th, 14 (PH), 16.5 (Fiz), and 16.5 (UA) and at 17th, 17.5 (PH), 22 (Fiz), and 22.5 (UA).
Of course, averages only say so much. If you go by Max, Fizban looks better at 17th: 30 (PH), 40 (Fiz), 27 (UA) but a far more interesting thing is happening: minimum damage. Again at 17th: 5 (PH), 4 (Fiz), 18 (UA). The floor is significantly higher due to the static level bonus.
Another thing to look at: UA's breath weapon improves with every level, not just the checkpoint levels. Compare a 16th level dragonborn who is still doing 14 or 16.5 to a UA who is doing 21.5 and you'll see UA pulls ahead for a while before the other db's get a chance to catch-up.
The only net loss is replacing an attack with a breath, which does lower DPS overall. But you trade that for more reliable floor damage at a slight loss of top end.
EDIT: the shape also matters. PH breath shape is determined by type, Fizban is a 30' line (good for stacks or avoiding allies, but rarely hits multiple targets) while UA is a 15' cone, which is easier to aim at multiple adjacent foes at the cost of friendly fire. That being said, it's easier to hit multiple targets with burning hands than with lightning bolt, so that is something else to consider.
You also get darkvision (something they always should have had) and free draconic language to make up for the lost chromatic/metallic/gem traits. Not great, but far better than 2014.
So I don't think the dragonborn is as bad as it appears. Maybe even a little better?