WordPress is still mangling my HTML

I am posting some help files that were created in HTML into WP pages, and when to the visual editor to update the graphics its mangles the lists.

Doing a search on this, I find that there are people complaining about this back to 6 years ago and basically nothing has been done to address these problems.

https://www.ads-software.com/support/topic/html-editor-is-mangling-my-code?replies=4

https://www.ads-software.com/support/topic/wordpress-mangling-html?replies=8

I’m just a simple user, but the WordPress organization ought to be embarrassed by this type of non-attention to problems. What good are fancy new versions with all kinds of features if you can’t get the basics done right?