People do a variety of things.
Some do as you thought, hide the Blizzard frames and create their own ones.
Other's change the visuals of the Blizzard frames but keep the functionality as is.
Many use the libs you mention to ease some of the workload.
Here;s an example of what is likely a simple addon.
https://www.wowinterface.com/downloa...nsRemover.html
This one might be a bit more complex and may or may not utilise libraries.
https://www.wowinterface.com/downloa...ClassicUI.html
Give them a look see and hopefully some other responses will add more info to help you.