If you have a style indicating a few basic tenets, where "ki-ryoku" seriously only referred to "spirit", then you would have essentially a dumb style, so to speak, and they weren't dumb.
I'm sure way back in the day, the creators of kendo were true masters of old-school kenjutsu and knew what they were talking about when they said "ki'... but modern kendo is now somewhat far removed from its roots. A modern kendo master in the standard kendo context
saying "ki" very likely means "spirit"; however possibly when they speak in the kenjutsu context it definitely could mean body skills.
From what I can see of modern kendo, the physical aspect can be covered with conventional muscle, but the mental aspect has levels upon levels of pure mind-skill ("spirit") which is awesome to see at high levels. Unfortunately body skills is a bit of a third wheel in this particular budo: you don't actually need all that whole-body short power to be really, really good at kendo regardless of your age, physiology etc... unlike no-rules real slice-and-dice combat kenjutsu. So in a way kendo really is a "reduced" version of kenjutsu... but training the mental game more than the physical makes it more relevant to modern life, and great fun too.