Nonetheless, it would also lead to higher concentrations of votes on fewer accounts
In some sense that is the idea since self-voting is the opposite of that.
The real question is one of degree. You don't want everyone voting for themselves (maximum spread across maximum accounts) but you also don't want too much concentration that doesn't help the value of Steem (that being said, very high value contributors with a large audience are indeed worth a lot in what they bring and give back, which is why such people are paid a lot on other platforms).
All that being said, curation itself doesn't necessarily encourage extreme concentration of votes. Once there are a lot of votes on a piece of content, voting for it will earn sub-par curation rewards. To maximize curation, you are better off finding something else that isn't heavily voted yet.