Okay, thank you. I will try it. I appreciate your speed in getting back to me, and your time in responding.

I've tried it this way as well though- with and without quotation marks. The Minecraft prefix was the second thing I tried, after which I tried an Essentials prefix, and then no prefix and quotation marks (like the wiki) again.

You don't put prefixes in the command-block-overrides section.
Just 'tp' works fine -> I just tested it.
You can use '*' to force all Vanilla commands to take priority.

This doesn't seem to work. :/ I've followed the syntax of the wiki previously (quotes around the command), and the game changed it. Either in command blocks or in-game (where I intend it to work), the commands default to Essentials no matter what. 

I know this isn't necessarily the place for this, but I'm just not finding a lot of support online- no sample configs showing how this really works, just contextually removed snippets.

My solution has always been to prefix my commands. I ran this by Mojang as well, and their response was that I should take it to the "modded" community.

I've tried these commands with no prefixes, with essentials prefixes, and with Minecraft prefixes, all to no avail.

No Minecraft prefix.

command-block-overrides: []

This is the option in commands.yml you should use to select which command is used.
Its hard for us to support prefixes because Mojang requires that the commands exist when the function is loaded.

You can use command-block-overrides: ['*'] to force vanilla commands always.