They were probably first to market, but then the community found the RCM bug and now Xecutor is pretty irrelevant.
Side note: “So long Gary Bowser“
Well, irrelevant for people who own a Switch that's vulnerable to the RCM bug. Nintendo fixed that in a hardware revision around two years ago so there's a lot of Switches out there which cannot be hacked by the open source methods, but can with Team Xecuters hardware mod. RCM was patched before the launch of the "Switch 2.0" and Switch Lite, so the only way to get homebrew along with the improved battery life of the 2.0 or greater portability of the Lite is via that hardware mod.
Edit: XenoGC!
IIRC the XenoGC was originally proprietary too, but open sourced by the designer after a few years.
I think they changed it for Super Mario 3D All Stars.
That version added rumble support and fixed some bugs, but being intended for Japan where Bowser is called King Koopa they used a different voice line.