In this case, as they were running into the automatic GC interval, their program did not create much, if any garbage. So the CPU overhead for the GC would have been quite small.

If you do a lot of allocations, the GC overhead rises of course, but also would the effort of doing allocations/deallocations with a manual managing scheme. In the end it is a bit trade-off, what fits the problem at hand best. The nice thing about Rust is, that "manual" memory management doesn't come at the price of program correctness.

Languages that have GC frequently rely on heap allocation by default and make plenty of allocations. Languages with good manual memory management frequently rely on stack allocation and give plenty of tools to work with data on the stack. Automatic allocation on the stack is almost always faster than the best GC.

GC languages often do and also often do not. Most modern GC languages have escape analysis. So if the compiler can deduct that an object does not escape the current scope, it is stack allocated instead of heap allocated. Modern JVMs do this and Go does this also. Furthermore, Go is way more allocation friendly than e.g. Java. In Go an array of structs is a single item on the heap (or stack). In Java, you would have an array of pointers to separately allocate on the heap (Java is just now trying to rectify this with the "record" types). Also, structs are passed by value instead of reference.

As a consequence, the heap pressure of a Go program is not necessarily significantly larger than that of an equivalent C or Rust program.

Escape analysis is very limited and what I found in practice, it often doesn't work in real code, where not all the things are inlined. If a method allocates an object and returns it 10 layers up, EA can't do anything.

In contrary, in e.g. C I can wrap two 32-bit fields in a struct and freely pass then anywhere with zero heap allocations.

Also, record types are not going to fix the pointer chasing problem with arrays. This is promised by Valhalla, but I'be been hearing about it for 3 years or more now.