I just tried to use Cortana to add an appointment to my outlook calendar. Yuk. It was clunky and worse it didn't get the date or subject right.
Compare that to my google phone which gets it right 99% of the time and is easier to use. Microsoft Cortana is way behind, but they will catch up.
Although Google is the best at voice recognition and understanding what I want, I still talk to Alexa more. The reason? I don't have to press anything. Yes, I have "OK GOOGLE" on my phone but the phone still has to be awake (screen on) for that to work. I suspect they'll fix that at some point but for now Alexa wins the simplicity battle.
I use Alexa a lot. I was starting to regret buying the Tap last year after buying the DOT this Christmas. The always listening feature is really simple and has me adopting more interaction with Amazon. I've even started buying supplies via Alexa. I was in the kitchen realizing we were almost out of dog food when I thought, "I'll try Alexa" and told her to reorder. 5 seconds later I was done. Then I re-ordered 2 more things I might have run to the store for instead of buying from Amazon.
Whatever you are building, you have to keep it simple to build momentum. Once people use a tool, they'll ask for more. It still has to work well (Siri is still very flawed) to be useful which is another reason Alexa kept their features limited at first.
As they've taught for years, Keep It Simple Stupid works now more than ever.