If they'd hire the right person, they could have Siri in the top 3 of assistants within the timespan of a perhaps few months. It's not rocket science anymore and in fact most of the underlying tech is already open source.
Products at Apple have to meet a high bar for all of: Privacy Compliance,Public Relations+Marketing alignment,World Class R&D,Focus Testing,UAT and Deployment on billions of devices. I don't see how one person could make that big of an impact. And in a few months? Somehow I don't think you thought this statement through very well.
I agree, but we’re still talking about five years for a huge company with colossal cash reserves. Surely one person won’t cut it to do all the work, but I’d wager that the person overseeing the Siri department isn’t doing their job very well. Sounds more like there are managerial/political issues rather than technical ones.