I suspect the new training status stuff that’s been rolled out would likely be a good fit for cyclists, even those who haven’t purchased a power meter.

Generally Garmin has much better features than Strava for setting up and executing a structured training plan, then analyzing your performance. But Strava has better social features. Many endurance athletes use both platforms. It's easy to create a free tier Strava account and automatically sync activities from Garmin to show your friends.