They also ran iOS without really much adaptation for the form factor. Now it's called "iPadOS" and has functionality that differentiates it from an iPhone. You can even dual screen the thing if you're a weirdo.
I love using it as a second screen when I’m out at a coffee shop. It works so seamlessly and I can throw Slack on there while I code, without looking like a complete weirdo
Sidecar works surprisingly well. With its latency and performance it’s barely distinguishable from a wired screen even running a HiDPI resolution.
If you want, it's possible to wire it up too! I use the included USB-C cable to connect it directly to my MacBook. It's much more reliable that way, especially if you're on a flaky WiFi connection.