Those are two completely different programs. balencaEtcher is for flashing an ISO to the USB stick. Basically its like installing an operating system on your hard drive, but it installs it on the USB drive. It will make it bootable. If you want a different OS, you have to completely flash the drive and replace whats there.
Ventoy will also make the USB stick bootable, but it will not flash an operating system onto it. It’s more like a general launcher of ISO files. This means, you only install Ventoy once and then can drag and drop ISO files to a folder. If you boot Ventoy from USB stick, it will show a list of all available ISO files. Choose one and it boots into the distribution, like you would have flashed it with balencaEtcher.
The advantage of Ventoy is clear: Easy replaceable ISO files and having many to choose from withing a single installation. Filenames of ISOs doesn’t matter and they can be placed in sub directories in the ISO folder I think. Ventoy will just list all available ISOs you can choose and boot into. The disadvantage is, that some distributions or hardware might not work well with Ventoy, but that’s not my experience so far.
I want to use Glim too, because the binary Blobs in Ventoy are bugging me a lot. But Glim is a bit limited still: README