Yep. At least, thats the slowdown rate I saw porting my own (very optimized) CRDT to wasm last year. I haven't measured automerge's wasm build but 3x slower is a reasonable baseline for wasm's performance compared to x86_64 code.

Some of that difference is a lack of auto-vectorization in wasm. Wasm SIMD is pretty new, and not well supported in wasm runtimes yet as far as I know.