Reducing the vote number doesn't really do this, because the total vote weight applying to the elected witnesses (i.e. #20 threshold) would certainly decline by a lot. It then becomes easier all else being equal for one large stakeholder to elect some witnesses even if not all of them, and (depending on the numbers) may or may not actually be harder to elect all of them (using multiple accounts)

It isn't great that the votes needed to get into the top 20 is currently a bit on the low side (IMO) but this is mostly a function of so much of the supply being held on exchanges as as well as a certain amount of non-voting (apart from steemit itself). Though even the current low number is much too high for any non-steemit stakeholder to choose witnesses unilaterally.