I primarily used Kakoune for 2 months a few years ago. I loved its featureful regex engine which made certain macros much MUCH easier to write than Emacs functions. I also loved the selection-first editing model and have reimplemented that in Emacs and VS Code. But Kakoune was far too basic for me to get much serious C++ work done. You have to use external TUIs and CLIs constantly, and obviously those all have no integration with your Kakoune configuration.