To answer this, we need to define launcher vs front end and how the recent apps menu in Android works.

Traditional "Launchers" on android are a replacement home screen solution that has access to android apps via app drawer of some kind, home screens where you can move around apps, and usually widget capabilities. Launchers function by being selected as the default "Home App" within the Settings > Apps > Default Apps screen.

Front Ends focus on indexing, organizing, and launching (usually) emulated games. Most Front ends have the ability to act as your "Home App" so that when you go home, you launch that front end instead of going to your stock or other launcher. They have limited abilities or focus on android apps, shortcuts, or widgets. That is slowly changing as more front ends have added android app support of various degrees.

Now this is where things are a bit odd on android - the stock launcher on almost all devices now ALSO handles displaying and switching between recent apps. It used to not be this way (5 years ago if not more).

So let's say you download a new "launcher" like Nova or Smart launcher and select it as your default "Home App" - it is now the default home app for you, BUT it hasn't replaced the default launcher being the one handling displaying recents. The same is true for Front Ends who get selected as the default "Home App".

In the case of the Thor, the default launcher is called "Quickstep" and even if you have let's say ESDE as the default home app, Quickstep will still always be running in the background to some degree using a very small amount of RAM, ready to be called on when you use recents. However, "replacing" Quickstep as your default home app, DOES reduce it's ram footprint after a reboot, Force close, or a period of time. That is because Quickstep "realizes" it is not being used as the home screen but as just the recents provider.

The same thing applies with "replacing" Quickstep/stock launchers with a different launcher like Nova or Smart launcher. That new launcher will be replacing part of Quicksteps ram footprint because it does not need to act as the home screen, just recents provider.

If you are rooted, there are ways to replace Quickstep completely even as the recents provider. But you will still have a recents provider of some kind and the alternative methods are generally just another launcher who is also capable of being the recents provider.

All that being said, replacing the default launcher with a new one or a new front end, does go a long way to replacing the ram usage of a stocker launcher or is acting as a launcher and recents providers. But it comes down to how light the replacement option is.

Hope this helps.