I think Garmin reasonably sees Strava as a boon to their business. Before it came out, most cyclists had simple odometer style bike computers rather than gps devices. GPS computers existed but there wasn't much you could do with the data. Strava should likewise see that services like Relive only increase customer satisfaction and engagement with Strava, especially given that Strava doesn't have the technical wherewithal to add new features, like, ever (my personal suspicion is that all engineers are constantly in a performance code red, trying to get hosting costs down).