There is no difference, among the 9 justices, that Bellei was naturalized and was a full fledged citizen at birth, and all agree he would be a citizen today if he had 5 years residence in the US before reaching the age of 21.
What you term as a third class of citizen, is what the dissent sees as a full fledged citizen whose citizenship can be stripped by Act of Congress, after the Act grants it. The majority said Bellei was naturalized, but not IN the US, so didn't get 14th amendment protection. The dissent said that the location, or where he was naturalized was immaterial, and Bellei should be, as a matter of law, covered by the 14th amendment.
A citizen covered by the 14th amendment is either born in the US or naturalized.
Not presented for argument, I accept your invitation to part ways. Presented only as a brief restatement of the case. The case that would not and could not exist, but for the fact that Bellei was naturalized.