I do mean the price of steem, and you're right it doesn't depend directly on an individual's action, but on the aggregate of all user actions. When there is a high ratio of self-vote/curation, we should probably expect to see the price of steem go down. Whales do have more influence on that aggregate than minnows.

I just don't understand why there such a huge gap between rewards.

If I understand your question, the gap between rewards is probably because the self-voter collects author rewards and curation rewards, but the curator only gets curation rewards. They could close the gap by posting some comments or articles and getting author rewards via upvotes from others.

I have also seen a post suggesting an increase in the curation reward percentage. That wouldn't eliminate the gap, but it would shrink it.