I think the model is changing as I wrote in my latest post. Those with STEEM are starting to delegate to different projects. It is the projects that are doing the upvoting.
And all in all, the larger accounts do not create a ton of content. Look at the top 50 accounts and you see they rarely post...a couple times a week at most.
As more newer people come on, collectively the larger accounts start to lose their power since a larger portion of the reward pool goes to the content creators. We already saw a big shift the last year. I expect, when more people sign on in bigger numbers, this will even be more pronounced.