You could try a 3rd party application that supports double-tap to wake without having to enable Ambient Display. Tiles
https://play.google.com/store/apps/d...settings.tiles may be a possibility (I'm currently looking to see if it'll do what you want, but it is a paid app and requires setup using ADB). There are lots of others in the Google Play as well.
Edit: well, after setting up that 'Tiles' application it turns out that it won't give you what you're looking for. The double-tap implementation is the same as the built-in solution, so it takes you to the Ambient display screen (even though that's turned off) rather than directly to the Lockscreen. Sorry, guess you'll have to look for other 3rd party solutions.
Be sure to provide feedback directly to Google about your dissatisfaction with the operation of this feature.