I would say 90% of the struggle of my learning to play piano was developing the correct muscle memory for the right motions for the right measures of the right

I would say 90% of the struggle of my learning to play piano was developing the correct muscle memory for the right motions for the right measures of the right song. The academic "Can I read and understand this sheet music?" is maybe 10%. It's possible if you put in the decades required to build up all the muscle memory needed for any song you might need to play (or you are a virtuoso), in which case reading and understanding the sheet music may be 90+% of your "practice time"... but the most accomplished pianists I know of still have to practice (with their hands) consistently.