I can think of various langages where string is not a built-in, but i can’t think of a langage where string is not some sort of sequence, not just in its implementation but in its interface.

The definition also breaks down quickly e.g. is a complex a primitive? If not because they have real and imaginary parts, why are floats which have a mantissa and an exponent? And what about functions? What even is a child? Are value-less sum types primitives but valued ones not?

More importantly, how does it matter? What does the distinction you draw provide that is useful?