From the horses mouth, I had seen this posted on a GCN Facebook group:

https://support.strava.com/hc/en-us/...bile_site=true

Yes, seems that they now are expecting new users to use another app and then upload to Strava. I think this will hurt their incoming new user base however. In fact, the person who posted it had switched to the Wahoo app and dropped Strava.

I know I used the phone app for years, including using a HR and cadence sensor, before getting a dedicated GPS computer and still do depending on the bike. Not having the ability to collect sensor data probably would have made me use a different app back then.