That is true - according to the 1945 amendment.
However, if you check the most recent amendment (2003) that we have access to...
As far as I can see the 2003 re-statement is for the WTBTS of New York and the 1945 amendment is for the WTBTS of Pennsylvania. These are separate corporations and the Pennsylvania corporation is the primary one which offered shares to the public and which were dissolved into voting shares for the 500 appointed voters.
However I guess it would make sense for them to also have changed the Pennsylvania corporation in the same way (using bylaws for election), but unfortunately that document is not yet publicly available.
The heart of your reasoning comes down to this:
Let's imagine that some of those nonJWs are...let's see...bloodless surgeons....Would it be in the interest of people who work in bloodless medicine to have the WTS drop their blood doctrine? No, it wouldn't. But, keeping that doctrine in place would pay 'dividends' to the bloodless industry and anyone connected to it.
Well the GB control the doctrine and so I read up on what the Watchtower says in this regard. Since 1971 the voting members no longer even re-elect the governing body at all (I did not know that). Since then (1971) the GB elect their own members by themselves:
"In 1971 the same speaker explained that the members of the Watch Tower Society could not vote in the members of the anointed Governing Body. Why? “Because,” he said, “the governing body of the ‘slave’ class is not appointed by any man. It is appointed by . . . Jesus Christ, the Head of the true Christian congregation and the Lord and Master of the ‘faithful and discreet slave’ class.” Clearly, then, the members of the Governing Body cannot be voted into office by the membership of any legal corporation."