The top 12 accounts (minus steemit) that have activity within last two years hold 35% from the query I pulled for steem alliance voting. I did forget to remove misterdelegation and steem though, so that is going to be lower. But... Still gives you a pretty good idea.

If you look at account counts and stake %. So two more in that top bucket needs to be factored out but relative number wise that's how it looks.

The way I see it, everything is still proportional to stake and we will see quite a different distribution of posts. I do believe that 25% is not enough for the top few to lock down the rest of the system. And keep in mind the top accounts don't necessarily see eye to eye, so that helps too.