You have to define which axis' you're using to define efficient. If I were an executive at some corporation, I'd tell my assistant to book me a flight to New York on Friday at 7pm and that takes me less than 10 seconds. It may take her a while longer, but that's her problem and that's what I pay her for.
How long is it going to take you to get to a device, load the app/webpage, tell it which airport you're flying from and going to and what date and then you start looking at options. You've blown way past the 10 seconds it took for that executive to get a plane flight.
Better is in the eye of the beholder. What's monetarily efficient isn't going to be temporaly efficient, and that's true along a lot of other dimensions too.
Point is, there are some people that like having conversations, you may not be one of them. you don't have to be. I'm not taking away your mouse and keyboard. I have those too and won't give them up either. But I also find talking out loud helps my thinking process though I know that's not everybody.
the inferior methods were slower but more flexible - could handle any and all edge cases. Currently we have a UX that really efficiently realises 80% of cases.
To relate to the article - google flights is the Keyboard and Mouse - covering 80% of cases very quickly. Conversational is better for when you're juggling more contextual info than what can be represented in a price/departure time/flight duration table. For example, "i'm bringing a small child with me and have an appointment the day before and I really hate the rain".
Rushed comment because I'm working, but I hope you get the gist.
Current flight planning UX is overfit on the 80% and will never cater to the 20% because cost/benefit of the development work isn't good
The whole point is that we currently have better, more efficient ways of doing those things, so why would we regress to inferior methods?