From what I've read, that 'At a Glance' widget is permanent on the Pixel launcher. Changing the default launcher is the only method I know of to circumvent it.
Doesn't change the ugly notifications/clock style on the lock screen though, or the goofy shapes widgets that Google pre-loaded elsewhere, either. What's Google thinking? Is it still 1976 where they're at? All they need to make it more 1970s is add in some fonts like the ones Burger King is using today to complete the set!