For me, I only consider using an app if it is cross-platform, especially if it is a communications app. So Facetime will send links to
Android and Windows users now (really links don't work on Linux???) so that these users can join Facetime calls. But the point is Android and Windows (and Linux?) users cannot initiate Facetime calls to their friends. This basically cripples Facetime usage for most who have friends, colleagues and clients that don't all use iOS.
I was also hoping for RCS to be included in iMessage (again for cross-platform modern messaging across Android, iOS and other devices). It may be though that with RCS fully adopted that could cripple WhatsApp and similar messengers (well Apple has made major swipes already at Facebook, so I'm sure they'd not back away from taking a swipe at WhatsApp).
Other items of interest to me from Apple's WWDC 2021 were:
* Existing iCloud services will, at no extra cost, get a VPN service (Private Relay) and private e-mail (basically unlimited extra iCloud mail addresses which forward mail to your primary address).
* Digital identification to start for certain airports and US States but like Apple Pay should hopefully spread elsewhere soon.
* The Health app will more easily identify trends and changes over time, including mobility tracking and capturing a new walking
Steadiness Metric to assess your fall risk. Also seems like they will not just capture your cholesterol (and other) scores, but go a step further now to help interpret what the changes mean.