I find comments like this illustrate perfectly the gap between these focused on language theoretics, and those focused on building software.
Go is successful because it strikes a strong balance between what practical software engineering organizations need from a language, of which safety is only one constraint.
Languages also need to be: * Easy "enough" to learn * Easy to read * Easy to write * Performant * Compile quickly * Have strong tooling * Have a strong standard library * Provide good solutions for it's problem domains * Support large code bases with many dependents ... * And be "safe*
Easy here is also influenced by what people already know, syntax and basic working methods need to be familiar to the vast majority of software engineers.
Go is successful because for many engineers it provides enough of all of the above with *enough" safety.
P.s. complex, difficult to understand languages incur more bugs then simple ones, even with additional safety.
PPS: If you think multiple returns and sumtypes solve the same thing, you've not thought very hard on the subject...