you should be able to understand  that it CANT be ALL on the mainchain.  There are diametrically opposed requirements.  Like anonymity vs. public spending accountability.  Like handling vast numbers of txns per second vs. keeping all transactions forever.  Like blockchain spam vs. document timestamping.  There are plenty of things with diametrically opposed requirements in life, like sleeping (darkness) and reading a book (bright light); its unrealistic to imagine no 2 applications will emerge in a space which covers the entire concept of economic activity.