Isn't the memory barrier a huge penalty? (WASM can only access it's own memory, never the hosts.) I've been thinking about how WebAssembly could work server sid

Isn't the memory barrier a huge penalty? (WASM can only access it's own memory, never the hosts.) I've been thinking about how WebAssembly could work server side to host websites, but every step seems to be copy bytes into or out of the VM.