Going from something like "Go lacks a builtin arena allocation" to "Go risks becoming the COBOL" is a long stretch. First, Go is slower than C/C++/rust without complex memory allocation. Introducing an arena allocator won't fix that. Second, arena allocation often doesn't work for a lot of allocation patterns. Third, plain arena allocator is easy to implement when needed. Surely a builtin one would be better but Go won't fall without it.