Yes. Leading tone usage and such were derived from his chorales. There is a 97% consistency in his resolutions, cadences, et cetera, and it sounds good.
Theory follows practice. He made it up, and now it is considered standard practice for major-minor “Classical” (really starting with Baroque) harmony.
Fortunately, some of his chikdren, Wolfgang Mozart, and especially Felix Mendelssohn, helped preserve what became the backbone of modern “serious” music. It could have easily been lost.
That is so interesting! I know very little (read: almost nothing) about musical theory, but I love to sing and love to hear great choral singing.
It’s amazing how one creative person, or a very small handful of people, can have a huge, multi-generations-long impact on the music of their nation and their age, and beyond that their world and for all time, per omnia saecula saeclorum, amen.
These guys are as blessed as saints, in my thankful estimation.