Not at all true.

I cannot track my heartrate on my phone. I can't take an ECG. I can't track exercise stats. I can't use Apple Pay with authenticating in some way.

It's much easier to control music and podcasts on my watch when out for a walk. It's much easier to see messages. It's much easier to send messages, set reminders, timers.

Anytime I can do something without taking my phone out of my pocket is a win for me.