Complex sentence: Numerically most businesses in the U.S. are not corporations but unincorporated sole proprietorships, however this is NOT an indication of the portion of the economy or labour market that falls within corporate or joint stock company control.
Split into simpler sentences: Numerically most businesses in the U.S. are not corporations but unincorporated sole proprietorships. However this is not an indication of the proportion of the economy or labour market that falls within corporate or joint stock company control.