It's certainly better than Go's (Go's is barely better than C's and that's quite a low bar), but I don't think that sum types are the global optimum.
Exceptions are arguably better from certain aspects, e.g. defaulting to bubbling up, covering as small or wide range as needed (via try-catch blocks), and auto-unwrapping without plus syntax. So when languages with proper effect types come into mainstream we might reach a higher optimum.