OK beej67, a sole proprietor has low overhead. Great observation of the obvious. What exactly is your point?
A bill-out rate equals salary plus payroll burden plus overhead plus profit. Salary and payroll burden (payroll taxes, benefits etc.) are real costs. So is most of the overhead: insurance, heat and light for the office, promotion/marketing so customers know who you are etc. Drop your overhead by eliminating typists etc. and making better use of technology, and you can either choose to drop your rate and hopefully pick up more business, or keep it where it is and make more profit.
If your argument about the "multiplier" as "taxation" is that the overhead is staying the same despite the decrease in admin staff etc. because the professional management are paying themselves more, or wasting the money on stupid unproductive corporate BS, I guess that's the shareholders' business and they should hire better directors or invest in something else. It's also the customers' business: they can shop for lower rates if they want.
As a company we'll use sole proprietors for some things, while others we'll want a firm with some assets and some depth to do for us. That's unlikely to change due to the "cloud".