This is correct. Thumb-2 is the only actual compact instruction set in wide use. x86-64 doesn't even come close to being as efficient; between ARM and x86-64, it's a wash.
It's certainly possible to design a CISC ISA (or maybe even a RISC one) that's optimized for compactness. x86 isn't that, though. Maybe it was in the 16-bit era, in a hypothetical future where BCD instructions were used a lot.
