This of course utter nonsense. There's nothing different about the performance of compressed instructions.
The cost in area and power of a decoder for variable-length instructions increases faster with the number of simultaneously-decoded instructions than the cost of a decoder for fixed-length instructions.
This makes the compressed instruction encoding incompatible with high-performance RISC V CPUs.
For the lower performance required in microcontrollers, the compressed encoding is certainly needed for adequate code density.
The goals of minimum code size and of maximum execution speed are contradictory and the right compromise is different for an embedded computer and for a personal computer.
That is why ARM has different ISAs for the 2 domains and why also RISC-V designs must use different sets of extensions, depending on the application intended for them.
Decompression is part of the instruction decoding itself. It only requires a minuscule 400 logical gates to do.
In fact RISC-V is very well designed for doing out-of-order execution of multiple instructions as instructions have been specifically designed to share as little state as possible. No status registers or conditional execution bits. Thus most instructions can run in separate pipelines without influencing each other.