I've watched parents set up every parental control imaginable—app limits, bedtime blocks, content filters. And within a month, the kid's found a workaround or the parent's exhausted from playing tech-support jailer. That's the thing about your "parents can manage it easily" point: it sounds good until you're living the daily negotiation over screen time. Every block becomes a battle, and the parent becomes the enemy instead of the ally.
The bigger issue is that even a monitored phone changes a kid's headspace. Just knowing it's in their pocket makes them check for notifications, and that anticipation alone fractures attention. There's research showing the mere presence of a phone reduces cognitive capacity, even when it's off.
You said they need to "keep up with the world." But a ten year old's world is playgrounds, classrooms, and family dinner. A smartphone doesn't connect them to that—it pulls them out of it. Let's give them the world they actually have.