I keep seeing people say this but I don't agree. There have been times when Alexa doesn't get me an answer where Siri does and vice versa. As for the home control functionality, saw an article somewhere that addressed this. The Echo/Alexa system is more open where Apple's homekit is not. Developers were quoted saying Apple's system was slower to grow mainly due to the tight controls Apple is known for. They actually appreciated that more and felt in the end Apple's system would be more successful. It's kinda like the Apple/Android situation.
I use both. The Echo is great for sitting in a busy location since anybody can use it. It also has more skills, which gives it a few features you don't get on Siri.
However, Siri is on my wrist everywhere I go and controls Apple Music in my car and at work. I find them both to be very useful, but if I had to live with just one of them it would be Siri. It is there all the time, which means it is there with almost no effort when I need it. Apps like Reverb are definitely a step in the right direction, but there is still a gap between the usefulness of Siri and Echo in my use case with Siri being ahead because of it being on my phone, watch and Mac.
Note: I tested it with the Plex app on my Nvidia Shield and it works great. I plan on using this quite a bit on my Mac, so I set up an icon in the Better Touch Tool (Touchbar) to put it at my fingertips.