I think there is a mistake in keil middlewares ver 6.x, keil should defines API functions for bottom layer of its middleware for micro/hardware interface and we as users can write our drivers according to keil APIs, keil can also provide this drivers layer according to stm32cube, but we as users can replace it with our custom drivers.
with this new keil method there is no way for user and we have to use stm32cube.Keil should give freedom to users to select stm32cube driver or user custom driver.
In current version you MUST use stm32cube + middleware or leave both and use your own middleware.
I hope keil modify its procedure for lower layer APIs and give us freedom to select drivers.