Look at the works of the late romantic composers. The rules, they still used, but widened the the extremest limits, got obsolet at some point, because if you use the rules or you don't use the rules, there's no noticeably difference. That's the point, where the Basis of all former rules, the classical cadenza, was thrown away by quite a lot composers (Debussy, Scriabin, Strawinksy, Schönberg etc.). Thats music history. Don't cry for the good old times, they never will come back. They never existed.