Yeah, very little of this is still true of the period in which the Neo or modern Chromebooks exist.

If the school is managing these Macs, including laptops sent home with a student, then unless it's for a specific purpose they aren't allowing you modify files, you probably aren't allowed to open a terminal or system settings, and you definitely aren't disabling SIP. You might not even be able to access the open internet if they've hard-configured it into a VPN. No different from a managed Chromebook.

Likewise, even older and lower-end unmanaged Chromebooks can enable a full Linux environment that runs a terminal in a browser tab. Doing so doesn't require root or developer mode, and it doesn't change or sacrifice any of the rest of the ChromeOS environment (for which your core assertion, that an unmanaged Mac is a computer and an unmanaged Chromebook is a thin-client appliance, still fundamentally holds). You can install Blender and have it running in a window by about 1 minute into watching a YouTube video titled "How To Download Or Update ANY VERSION Of Blender On Chromebook".

Gaining root on a Chromebook is mostly just a prerequisite to modifying things specific to ChromeOS, but the easier to access, more featureful, and safer LDE is still an entire operating system that you can tinker with, screw up, overload, blow up, and reset to zero, all without losing the happy path of opening up Canva (or, more likely, CapCut on their phone/iPad) and editing videos or whatever.

You don't have to root them to do cool shit anymore. They have a full Linux (Debian based) environment you can enable with a single toggle in the settings. Any GUI apps you install via apt get their icons dropped in the system tray and their windows are rendered via Wayland.

>the one I used in high school was locked down to basically a kiosk.

The Macbook Neo will be no different if the school is actually managing them properly.

macOS or Windows can be similarly locked down. In the schools, the school locks it down. In many companies, there are management tools like JAMF, InTune, or NinjaOne that lock down laptops, desktops, tablets, and cell phones a little or completely.