I'm under the impression that Go's original crypto libs were written by none other than djb himself. Is there a rationale for the deficiencies laid out in the OP, or am I putting djb on too much of a pedestal?
Bernstein was never involved.
Yes. The previous package had a dependency on the general purpose math/big package which was not constant-time and had a large surface area (that was not required for crypto). This has lead to security bugs in the crypto package.