I mean, I can. It's just an annoying pain in the ass, now, rather than a simple toggle. Which was a stupid decision on Apple's part.

Is it more or less annoying than having to dismiss the list of available wifi networks?

This change might be inconvenient for you personally, but I suspect there's no way in hell Apple would have made this change if they didn't have robust data on the way their average customer uses their device and didn't believe that this was a positive change.

Try "Hey Siri, turn off WiFi."

Five words isn't much beyond a simple toggle. :)

Ironically you possibly need WiFi (since siri operates remotely) to turn it off.