What's the difference from opening a Terminal (Admin) window? Just that you can run a single command as admin? I must be missing something here
What does Sudo is to only provide the root/admin privileges for specific inputted command. Once it is done, it goes back to user privileges. This way, the terminal window didn't need to end the session to go back to user privileges.
It also lets you elevate to admin without knowing the admin password, you elevate with your normal account password. Effectively, some commands can execute as admin, but the user generally cannot.
So you can allow limited administration without giving everything away.
Personally I think it's way more likely the admin command is the one off like installing something, changing a setting and then everything else before and between it are user commands that don't need to be in admin space most of the time.
I mean, that's sudo's whole thing! [1] You can live your day to day terminal life without the risk of borking things too badly, then when you occasionally need to elevate to higher privileges you can do it easily for that specific command.
[1] Technically not the whole thing obviously, but it's a very common use case.
The point of sudo is not which password is used, whatsoever.
It's a convenience thing.