Well most of Geany can be controlled from the keyboard without the mouse, the argument that you "have" to use the mouse is false, but because the UI paradigm (not modal) is different to Vim it will never be the same keyboard shortcuts as Vim uses. So the efficiency is available, but it needs re-educating the muscle memory to Vim, but non-Vimists find it more common and natural.
As I said above, if Vim users want a Vim UI then they need to step up and work on it as somebody did for the other editors/IDEs you mentioned (and I note Vscode/vim has 1000+ open issues), there is nobody else to do it, and as the originator of this plugin said on his webpage, its effectively making a totally new editor.
Geany is an all volunteer project so if nobody else in the Geany project is interested in doing the work for Vim users they need to do it themselves. Or of course perhaps adding the IDE features to Vim is possible.