Not sure I see the relevance here. We were discussing smart speakers you can compare home kit with smartthings or the other smart home bridges not with the Amazon or Google speakers.HomeKit supports all of these things and many, many more through the homebridge framework. Even if you aren't technically inclined enough to use homebridge, HomeKit is open now and it's only a matter of time before all of these are natively supported.
HomeKit also technically supports more device types than Amazon out of the box (Humidifiers, Air Purifiers, Sprinklers, Faucets, etc.)