Those new language constructs are exactly what's enabling the performance gains, by giving reliable information to the compiler. Projects like numba have clearly demonstrated the limitations of trying to compile pure Python.
It's only closed-source for now, with plans to open-source the language when it's more finalized - similar to LLVM early on. Not sure if it says so explicitly on their website somewhere, but Chris Lattner has stated that several times
I use the dwindle layout which is similar to bspwm in automatic splitting mode. One advantage is you can drag and drop windows into other nodes, which will be split appropriately, it's surprisingly neat when you have a lot of stuff open. It's easiest to get a feel for the differences by just trying it out or watching some videos of it on r/unixporn