The money that goes into the system are people willing to spend bitcoins or USD to buy Steem.
If no one wants to buy Steem, then even a million steem will be worthless.
So no matter how fairly it's divided between commenters and bloggers, neither will have much reason to even use Steemit, if they can't take their Steem out of Steem and spend it elsewhere.
Imagine this: The Steem produced on Steemit is for sale. Outside speculators buy as a total, USD $100 per day. This means there is only USD $100 to go around to all the content creators each day. There are 50 people total on Steemit.
If 10 of those people are bloggers, then they can each potentially take home $10 USD , give or take a few, and the commenters, the 40, take maybe $1 USD total.
This means that content creators make the money. Commenters make spare change. $10 USD per blogger is a fine amount to live on, right? That's lots of money per day, in this scenario.
But if we were to divide it equally, and all 50 people make lots of Steem, but there is still only $100 USD going into the system, it means that each person is only taking $2 USD home.
That's not enough to make a living on, which means that bloggers, people who are the ones who are supposed to make the good content upon which to comment, will go home. They don't want to fight over such tiny, spread out scraps.
This is how it would work right? If I'm imagining the wrong idea, let me know, but as it sounds, it sounds like you'd divide up the meager amounts of money flowing in even more than it already is.
This would make Steemit unattractive to serious bloggers.
Unless, like you said, it ends up increasing the people who invest in Steemit.
However, I think that late-game, it will be corporations that buy-in, in order to get people to subtly advertise their products and services. This means that comments won't be as important to the major corporate buy-ins, at least how I see it.
This would prevent them from wanting to buy in, if their buy-in has to be that much more to compete with the share of the reward that goes to commenters. It will take more SP to have influence over individual bloggers, which would reduce the size of major buy-ins, or completely prevent them.