You don't think the Sorceror physical transformations step on the toes of monstrous races (tiefling, dragonborn, etc) with similar qualities?
I don't.
For an example, look to the Breath of the Dragonsoul power granted by the Dragonsoul Heir paragon path in 4E. I wouldn't say it steps on the toes of the dragonborn. They have access to it, too; it would be yet another dragon breath attack for them, which I think most dragonborn players would enjoy.
As for the 5E dragon sorcerer (and, please remember that this is a single heritage we're talking about. It's not at all logical to assume that all heritages will have similar flavor--and that's really all it boils down to), we can't skip over some words, as many people are doing.
The sorcerer does not grow claws. It says that his hands grow claw-like (i.e. they look like claws, but they are not claws), and the body grows more imposing (which has no mechanical benefit, but I would flavor as a very minor manifestation of frightful presence). So, maybe the nails grow longer and sharper. Maybe they just "contort" to as close an approximation of dragon claws that the human hand can make (or maybe more, because the hand physically shifts somewhat, like the thumb more toward the bottom of the palm). It does not say that the sorcerer's hands become claws.
Later, the sorcerer grows scales over parts of his body--not the whole body, mind you, but parts. I'd imagine mainly over vulnerable areas, such as the heart, the neck, the stomach, the groin, and so on. If it were a dragonborn, I'd imagine the scales there would become real dragonscales temporarily.
Keep in mind that the dragonborn aren't dragons. They're not descended from dragons. They just look similar to dragons. I could see a number of dragonborn characters who would love this heritage so they could become closer to what they feel they are.
The infernal heritage (if it turns out the same way) will most likely be the same thing. Maybe that tiefling is going to look more like a pit fiend as the day wears on than the legion devil he resembles more in his normal form.
I'm excited just thinking of the possibilities when it comes to characters.