I think part of that illusion of speed is that the V2 SmartButtons do not really have any travel as they use a microswitch. You barely have to put any pressure on them to get them to fire an event. By the time they register a click, the event has already been sent.
That's not exactly slow... 195ms and that includes the message returned from the SmartPlug indicating it's turned off. That's under 1/4 of a second. I would dare say that without any scientific instruments, it's impossible to be any more granular than that when comparing the response times with iris.