I see your point, but I don't think 'owning 1 acc' as being a real limitation to your power. Justin could vote for 1 real account + 29 community witnesses and still use his power fully. Instead he did 20 dummy accounts and voted 20 times for himself. He's taking a shortcut, but essentially his total witness voting power (influence) remained the same number.

Also, you can see how making more than 20 wouldn't have changed anything. If he did that with 30, 40, 50 puppet accounts, it wouldn't optimize his strategy further.