Yep, that's the gist of it. In order to change the license from the GPL, they'd need the permission of all of the copyright holders who've contributed code under the GPL to the project. After a few months have passed, this basically makes it impossible (or at least extremely difficult) since at least one person (and likely many people) will say no.

Copyleft means: "if you modify the program and share it, you also have to include the source code for your modifications."

The owner of the copyright (usually the developers or their employer) can still change the license later.

AGPLv3 is not anti-business or anti-money. It's saying if you want to use the code in a closed source project you need to pay the copyright holder

The copyright holder is the original author, not a maintainer or someone who forked a project and renamed it.

That's why the #1 thing mentioned in copyleft licenses is you can't alter the copyright notice and declare yourself the original author

AGPLv3 is a good license to choose. All the other licenses are naive and do not combat closed source projects and the slave worker that keeps our projects unfunded

This URL might help you (I see it linked from the URL of this post): https://en.wikipedia.org/wiki/Copyleft

If it doesn't, I suggest looking at https://en.wikipedia.org/wiki/Wikipedia:Be_bold