I think the way I'd put it is that languages with manual memory management, like Rust, have more scope for optimization than languages that don't. You can just use the gc crate in Rust and have almost the same ease of development but the same performance problems you do in Go.
It also sounded like the developers had already thought carefully about their memory usage patterns and had been optimizing for performance as much as they could within the scope Go allowed them. Personally I've found Rust has a higher cognitive overhead than Go when I'm just banging something out only worrying about correctness but if you're thinking carefully about memory usage patterns in a way you need to to optimize performance there's no penalty.
