Normally, I’d agree regarding the 22LR but - a subsonic round coupled with a supressor would be a lot quieter than something more substantial. Quiet gives cover and makes the shooter’s position a lot harder to pinpoint quickly. Much more skill needed for accuracy, but not beyond the realm of someone that practices a bit.
then again, this was very likely a professional hit, and I would not be surprised if it weren’t orchestrated by some of the alphabet agencies that we all know and love (sarcasm tag).
You don’t need silence from a suppressor, you want an omnidirectional noise that fades in to background noise.