You obviously don't own an Echo. I am a huge Apple fan, but Siri is a pain in the ass comparing to Alexa on a stationary little Echo. I am giving command in normal voice across a huge room, while cooking etc. and it immediately activates and understands me perfectly. With Siri, I have to shout even if my iPhone is lying directly in front of me on my living room desk hoping that it will activate. Let alone that it understands me. Alexa is so much better as a voice assistent even in its first iteration (how old is Siri, around four years?) it's not even funny anymore.
I don't disagree with you about Siri at times being unresponsive. However, I find Alexa's voice to be incredibly slow and somewhat annoying, which is enough reason for me To not being interested after testing it. I know Amazon will improve the OS with Alexa, but truthfully, I still have good experiences with Siri being thorough enough for my needs and welcome changes coming, hopefully in iOS 11.