Well, maybe. When I ride, I want to know, in order of importance, my cadence, heart rate, time of day, and speed. After I get home, viewing a course map is nice but ultimately not necessary; all it's good for is showing off, IMO.
What my Garmin 410 gives me is GPS-calibrated speed, cadence, and quality heart rate data, with a configurable always-on LCD display. I can also leave my phone basically shut off, saving its battery over long rides.
What the Garmin is
lacking, however, is any tie-in with Apple Health. The UA Record app can get data from Garmin Connect (perhaps because of architecture purchased from MapMyFitness?), but that's only half of a solution as the Garmin workouts don't appear to get written into Health. Garmin has also thus far refused to add Health support for any of their devices besides their Vivo bands.
An Apple Watch, if it could have HR, speed, and cadence, would be pretty sweet. Another solution would be something like a Wahoo Rflkt set up with their HR strap and speed/cadence sensor (or better for me, the Rflkt+, so I can keep my Garmin ANT+ strap and speed sensor).
When OS 2 gets settled in and third parties build their native apps, maybe they can run an app to present all that data. The last hurdle, though, would be a continuous display while mounted on the handlebars… which I think is a job handled better by a basic, but larger, LCD display.